The loss of utilisable rangeland in semi-arid areas results in huge economic and social costs worldwide. Only adaptive management strategies are able to cope with these systems, which are largely driven by unpredictable and stochastic rainfall. Additionally they are characterized by strong feedback mechanisms between economic and ecological factors. This study aims to contribute to the identification of basic principles for sustainable grazing management. The approach emphasizes learning from existing management systems through the use of ecological-economic modelling. Two apparently successful management systems in Namibia are used as a starting point for a broader analysis: the Gamis Karakul sheep farm and the land use system of the semi-nomadic Ova-Himba. Although the economic systems differ strongly, their management seems to have similarities: the importance of pasture resting and of adapting livestock numbers to available forage. This PhD thesis contributes substantial insights about the relevance and functioning of pasture resting for sustainable grazing management in semi-arid regions. Assessment of the two case studies leads to the hypothesis that resting in the rainy season, particularly during wet years, is fundamental for ensuring pasture productivity under low regeneration potential of the vegetation. The thesis highlights that resting during wet years acts as a risk reducing strategy. Additionally, the study reveals that access to economic risk management strategies, such as rain-index-insurance, may change farmer´s behaviour towards less conservative strategies. The used approach - learning from existing apparently successful grazing strategies by ecological-economic modelling - offers a powerful tool for tackling new questions related to global change. The scope and the limits for generalizing the key factors discovered for sustainable grazing management can be easily detected under changing ecological, climatic and economic conditions.

Biomass is an important ecological variable for understanding the responses of vegetation to the currently observed global change. The impact of changes in vegetation biomass on the global ecosystem is also of high relevance. The vegetation in the arid and semi-arid environments of Kazakhstan is expected to be affected particularly strongly by future climate change. Therefore, it is of great interest to observe large-scale vegetation dynamics and biomass distribution in Kazakhstan. At the beginning of this dissertation, previous research activities and remote-sensing-based methods for biomass estimation in semi-arid regions have been comprehensively reviewed for the first time. The review revealed that the biggest challenge is the transferability of methods in time and space. Empirical approaches, which are predominantly applied, proved to be hardly transferable. Remote-sensing-based Net Primary Productivity (NPP) models, on the other hand, allow for regional to continental modelling of NPP time-series and are potentially transferable to new regions. This thesis thus deals with modelling and analysis of NPP time-series for Kazakhstan and presents a methodological concept for derivation of above-ground biomass estimates based on NPP data. For validation of the results, biomass field data were collected in three study areas in Kazakhstan. For the selection of an appropriate model, two remote-sensing-based NPP models were applied to a study area in Central Kazakhstan. The first is the Regional Biomass Model (RBM). The second is the Biosphere Energy Transfer Hydrology Model (BETHY/DLR). Both models were applied to Kazakhstan for the first time in this dissertation. Differences in the modelling approaches, intermediate products, and calculated NPP, as well as their temporal characteristics were analysed and discussed. The model BETHY/DLR was then used to calculate NPP for Kazakhstan for 2003–2011. The results were analysed regarding spatial, intra-annual, and inter-annual variations. In addition, the correlation between NPP and meteorological parameters was analysed. In the last part of this dissertation, a methodological concept for derivation of above-ground biomass estimates of natural vegetation from NPP time-series has been developed. The concept is based on the NPP time-series, information about fractional cover of herbaceous and woody vegetation, and plants’ relative growth rates (RGRs). It has been the first time that these parameters are combined for biomass estimation in semi-arid regions. The developed approach was finally applied to estimate biomass for the three study areas in Kazakhstan and validated with field data. The results of this dissertation provide information about the vegetation dynamics in Kazakhstan for 2003–2011. This is valuable information for a sustainable land management and the identification of regions that are potentially affected by a changing climate. Furthermore, a methodological concept for the estimation of biomass based on NPP time-series is presented. The developed method is potentially transferable. Providing that the required information regarding vegetation distribution and fractional cover is available, the method will allow for repeated and large-area biomass estimation for natural vegetation in Kazakhstan and other semi-arid environments.

Los corredores riparios en ambientes semiáridos mediterráneos son ecosistemas de gran biodiversidad y complejidad. En ellos confluyen una gran variedad de perturbaciones naturales capaces de crear un mosaico espacial y temporal con pocos paralelos en otros ecosistemas. Sin embargo, a pesar de su valor, los ecosistemas riparios están amenazados debido a los altos niveles de intervención humana. La construcción de presas (y la consecuente manipulación del caudal) está considerada como la perturbación humana más importante que se cierne sobre ellos. Esta tesis ha tenido como objetivo analizar el ecosistema ripario, abarcando diferentes escalas espaciales y temporales, y centrándose en los factores que influyen en la distribución, estructura, composición, calidad y dinámica de su vegetación, tanto en tramos naturales como hidrológicamente alterados de ríos mediterráneos, concretamente de la Demarcación Hidrográfica del Júcar (Este de España). Para lograr este objetivo, se han hecho los siguientes aportes a la investigación: A) Determinar los patrones de distribución de especies leñosas riparias en el gradiente transversal de la ribera y definir grupos de especies con respuesta similar a las condiciones físicas del hábitat; B) Comparar la respuesta de dichas especies en tramos naturales y alterados hidrológicamente; C) Definir curvas de respuesta y gremios hidrológicos de especies en tramos con régimen natural; D) Establecer los principales factores que determinan la calidad del hábitat ripario y fluvial y los patrones longitudinales de la composición florística, así como de las características del hábitat fluvial en un segmento hidrológicamente alterado; E) Describir los cambios espacio-temporales en la estructura y complejidad de la vegetación, y los cambios temporales en el régimen de caudales del corredor ripario de un tramo hidrológicamente alterado. Los objetivos anteriores fueron abordados con diferentes metodologías que implicaron la combinación de diversas fuentes de información y un esfuerzo importante en la toma de datos en varios lugares de estudio de los ríos Cabriel, Mijares y Serpis. Para cumplir con los objetivos A y B, se llevaron a cabo un muestreo de suelos y un muestreo georreferenciado de vegetación a través de transectos transversales al cauce en dos tramos naturales y tres regulados. Los datos fueron analizados con estadística robusta y multivariante. Para cumplir el objetivo C, el muestreo georreferenciado anterior (junto con un muestreo dendrocronológico) fue acoplado con un modelo hidráulico en los dos tramos naturales, con el fin de obtener la serie temporal de cotas del agua a la que habían estado expuestas cada una de las plantas durante su vida. La respuesta de las especies y su posible agregación en gremios hidrológicos fue comparada mediante estadística robusta en relación a la duración de la inundación, duración de la inundación durante el período de crecimiento, duración continua de la inundación, frecuencia de inundación y elevación de la planta respecto al caudal base. Para lograr el objetivo D, toda la sección regulada del río Serpis (desde la presa Beniarrés - hasta la desembocadura; 40 km) se dividió en segmentos. En cada uno de ellos se llevó a cabo un inventario de flora y se aplicaron índices hidromorfológicos. Los segmentos fueron agrupados de acuerdo a su composición florística y características del hábitat fluvial utilizando diferentes técnicas de estadística multivariante. Finalmente se discutieron los factores principales que controlan los patrones espaciales de la composición florística, las características del hábitat fluvial, la calidad del hábitat ribereño y la heterogeneidad del hábitat fluvial. Para alcanzar el objetivo E, se combinaron series históricas de caudales y su manipulación humana con imágenes aéreas históricas (reveladoras de cambios en la cubierta vegetal) y observaciones de campo de la distribución de edades de la vegetación y morfología del corredor ripario del río Mijares en los últimos 60 años. De esta información, se extrajeron métricas del paisaje e índices hidrológicos para identificar y resumir los cambios espacio-temporales en la estructura de la ribera y en el régimen de caudales. El estudio a escala transversal nos ayudó a comprender en cada uno de los tramos la zonación de las especies leñosas riparias en función de la morfología y características del suelo, revelando que la alteración del caudal puede influir en la modificación de los patrones posicionales de las especies. Se definieron tres gremios hidrológicos: ¿altamente tolerante a la inundación¿, ¿tolerante intermedio¿ y ¿de transición entre ripario y terrestre¿. El estudio a escala longitudinal sugirió que la respuesta de la vegetación a un cambio hidrológico es altamente dependiente de la geomorfología local. Se constató que los factores principales que determinan los patrones hidromorfológicos y florísticos son un régimen de caudales artificial y altamente variable (identificado en los segmentos con peor calidad del hábitat ripario y fluvial), la presencia de estructuras laterales en el cauce y las características geomorfológicas. Como efectos importantes de la regulación del caudal a largo plazo, el estudio a escala espacio-temporal reveló un aumento en la cobertura y densidad de la vegetación leñosa, una deriva en la composición de especies y una disminución en las áreas de sedimento desnudo (esencial para el reclutamiento de las especies riparias pioneras), junto con una reducción sincrónica en la complejidad de la ribera. Estos cambios estarían relacionados con la disminución de la magnitud y variabilidad de los caudales en las últimas seis décadas. Solo una mejor comprensión de los procesos ecohidrológicos y de las implicaciones de la alteración hidrológica sobre los ecosistemas riparios mediterráneos podrá apoyar la integración eficaz de estos sistemas en las decisiones de gestión del agua. / Garófano Gómez, V. (2013). Riparian vegetation patterns according to hydrogeomorphological factors at different spatial and temporal scales in Mediterranean rivers [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29395

Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C₃ Prosopis veleruina (mesquite) trees, whereas the burned plots are open C₄-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant -available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C₃ shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C₄ grasses to C₃ shrubs in surface soil layers. δ¹³C(SOM) values indicate that the Holocene and Late Pleistocene were dominated by C₄ grasslands, and the pre-Late Pleistocene vegetation was a C₄-grass savanna with abundant C₃ plants.

Chickpea (Cicer arietinum L.) production on the semi-arid Canadian Prairies is challenging due to a short growing season and low and variable moisture. The current recommended chickpea population density of 44 plants m-2 is based on preliminary studies and a narrow range of 20 to 50 plants m-2. The aims of this study were to i) determine optimum population density of varying chickpea canopy types, i.e., leaf type and growth habit, by investigating seed yield responses at 30 to 85 plants m-2 and ii) identify desirable parental traits for breeding programs by assessing growth and yield parameter responses to varying leaf types and growth habits at a range of population densities. Field experiments were conducted from 2002 to 2005. Canopy measurements and calculated variables included light interception, biomass, growth rate, seed yield, harvest index, ascochyta blight severity and radiation- and water use efficiencies. The plant density which produced the highest seed yield when averaged over years for each location for each treatment revealed that a plant density of at least 55 plants m-2 produced a 23% to 49% seed yield increase above that of the currently recommended plant density. This indicates that a higher seed yield average over the long term in spite of periodic low seed yield episodes will be more profitable to producers. Increasing plant density increased lowest pod height significantly in all except one location-year but did not explicitly increase ascochyta blight severity or decrease individual seed size. This suggests that increasing the recommended chickpea plant density on the Canadian Prairies will increase seed yield but would neither negatively impact individual seed size nor ascochyta blight severity, especially, when combined with good agronomic practices. Fern-leaved cultivars had significantly higher maximum intercepted light (62 to 91%), seed yield (136 to 369 g m-2), harvest index (0.33 to 0.53), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and lower ascochyta blight severity (3 to 27%) than the unifoliate cultivars in all location-years. The fern-leaved cultivars also tended to show significantly higher cumulative intercepted radiation (221 to 419 MJ m-2) and biomass (306 to 824 g m-2) but leaf type showed no consistent effect on radiation use efficiency. Cultivars with bushy growth habit generally performed better regarding maximum intercepted light (62 to 90%), cumulative intercepted radiation (233 to 421 MJ m-2), biomass (314 to 854 MJ m-2), seed yield (120 to 370 g m-2), harvest index (0.37 to 0.50), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and ascochyta blight severity (7 to 36%) than the erect cultivars. The overall performance of the spreading cultivar was generally intermediate between the bushy and erect cultivars except for ascochyta blight severity where the spreading cultivar exhibited significantly lower disease severity (3 to 36%). Radiation use efficiency was generally not influenced by growth habit. Increasing plant population density generally increased intercepted light, biomass and cumulative intercepted radiation on each sampling day after seeding resulting in a general increase in seed yield. Harvest index, however, remained constant and ascochyta blight severity was generally stable but radiation use efficiency decreased with increasing population density. Chickpea cultivars with fern leaves and bushy growth habit at higher than currently recommended population densities would best utilize the limited resources of the short-season Canadian prairie environment to maximize and stabilize seed yield.

Chickpea (Cicer arietinum L.) production on the semi-arid Canadian Prairies is challenging due to a short growing season and low and variable moisture. The current recommended chickpea population density of 44 plants m-2 is based on preliminary studies and a narrow range of 20 to 50 plants m-2. The aims of this study were to i) determine optimum population density of varying chickpea canopy types, i.e., leaf type and growth habit, by investigating seed yield responses at 30 to 85 plants m-2 and ii) identify desirable parental traits for breeding programs by assessing growth and yield parameter responses to varying leaf types and growth habits at a range of population densities. Field experiments were conducted from 2002 to 2005. Canopy measurements and calculated variables included light interception, biomass, growth rate, seed yield, harvest index, ascochyta blight severity and radiation- and water use efficiencies. The plant density which produced the highest seed yield when averaged over years for each location for each treatment revealed that a plant density of at least 55 plants m-2 produced a 23% to 49% seed yield increase above that of the currently recommended plant density. This indicates that a higher seed yield average over the long term in spite of periodic low seed yield episodes will be more profitable to producers. Increasing plant density increased lowest pod height significantly in all except one location-year but did not explicitly increase ascochyta blight severity or decrease individual seed size. This suggests that increasing the recommended chickpea plant density on the Canadian Prairies will increase seed yield but would neither negatively impact individual seed size nor ascochyta blight severity, especially, when combined with good agronomic practices. Fern-leaved cultivars had significantly higher maximum intercepted light (62 to 91%), seed yield (136 to 369 g m-2), harvest index (0.33 to 0.53), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and lower ascochyta blight severity (3 to 27%) than the unifoliate cultivars in all location-years. The fern-leaved cultivars also tended to show significantly higher cumulative intercepted radiation (221 to 419 MJ m-2) and biomass (306 to 824 g m-2) but leaf type showed no consistent effect on radiation use efficiency. Cultivars with bushy growth habit generally performed better regarding maximum intercepted light (62 to 90%), cumulative intercepted radiation (233 to 421 MJ m-2), biomass (314 to 854 MJ m-2), seed yield (120 to 370 g m-2), harvest index (0.37 to 0.50), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and ascochyta blight severity (7 to 36%) than the erect cultivars. The overall performance of the spreading cultivar was generally intermediate between the bushy and erect cultivars except for ascochyta blight severity where the spreading cultivar exhibited significantly lower disease severity (3 to 36%). Radiation use efficiency was generally not influenced by growth habit. Increasing plant population density generally increased intercepted light, biomass and cumulative intercepted radiation on each sampling day after seeding resulting in a general increase in seed yield. Harvest index, however, remained constant and ascochyta blight severity was generally stable but radiation use efficiency decreased with increasing population density. Chickpea cultivars with fern leaves and bushy growth habit at higher than currently recommended population densities would best utilize the limited resources of the short-season Canadian prairie environment to maximize and stabilize seed yield.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-09-21T18:10:08Z No. of bitstreams: 1 ADRIANO DE SOUSA BARROS - DISSERTAÇÃO PPGCS 2006..pdf: 18476854 bytes, checksum: 5c82955beb452edcc9bfde34a32b2307 (MD5) / Made available in DSpace on 2018-09-21T18:10:08Z (GMT). No. of bitstreams: 1 ADRIANO DE SOUSA BARROS - DISSERTAÇÃO PPGCS 2006..pdf: 18476854 bytes, checksum: 5c82955beb452edcc9bfde34a32b2307 (MD5) Previous issue date: 2006-09 / O Nordeste rural semi-árido tem passado durante as últimas décadas por diversos modos de pensar e fazer seu desenvolvimento e, consequentemente, sua modernização. Depois do amplo investimento em infra-estrutura na perspectiva do "combate à seca", acompanhado pelo plano de industrialização regional tido como a melhor solução para o problema do desenvolvimento da região, surge, na década de 1990, a perspectiva do desenvolvimento local e da "convivência com o semi-árido". Apesar de novo, esse olhar diferenciado sobre as dificuldades sócio-econômicas da região, aqui destacando sua porção semi-árida, trazem também em seu arcabouço um projeto de modernização, na medida em que propõe uma mudança de comportamento que afeta as estruturas sociais e produtivas locais. O Programa de Estudos e Ações para o Semi-Árido (PEASA) surge, em 1994, em meio a esse processo de mudança, propondo uma intervenção que altere o rumo do desenvolvimento de algumas localidades do semi-árido paraibano. Seu modelo de intervenção, atrelado à perspectiva dos Sistemas Produtivos Locais (SPL's), propõe por meio do agribusiness a criação de empreendimentos comunitários em forma de agroindústrias, nas quais os produtos de vocação local receberiam um tratamento logístico dentro de um amplo processo de racionalização da produção. O presente trabalho investigou esse modelo de intervenção, focando na construção de sua metodologia dentro da perspectiva de promoção do desenvolvimento local, buscando perceber também que perspectiva de modernização é construída a partir nas ações desse programa de extensão universitária. Nossa pesquisa utilizou-se de dados colhidos junto ao programa e seus colaboradores técnicos, na investigação documental (relatório de atividades, projetos defomento, artigos técnicos dentre outros); e no acompanhamento de uma de suas experiências de intervenção, o projeto de implantação da Agroindústria de Beneficiamento da Fibra de Sisal para Produção de Artesanato na Comunidade Cuiuiú, Barra de Santa Rosa - PB. O modelo de intervenção identificado como empreendedorismo comunitário mostra-se ineficiente na promoção do desenvolvimento local, chocando-se com o próprio sistema produtivo local de tradição camponesa e de organização familiar. O foco do modelo na racionalização das estruturas produtiva e social acaba por desconsiderar a questão ambiental, limitando o projeto de desenvolvimento às questões de cunho econômico. / During the last decades, the rural semi-arid northeast has gone through various forms of tliinking and making its development and, consequently, its modernization. After the wide investment in infra-structure aiming the "combat to the drought", accompanied by the regional industrialization plan, considered the best solution to the development problem in the region, in the 90's the perspective of local development and the living with the semi-arid carne to be. Despite being new, tliis differed look upon the social-economic difficulties of the region, hereby standing out its semi-arid portion, brings in its base a project of modernization, as it proposes a change of behavior which affects the local social and productive structures. The Program of Studies and Actions for the Semi-Arid (PEASA) appears, in 1994, in the middle of tliis changing process, proposing an intervention which alters the path of the development of some localization of the semiarid of Paraíba. Its intervention model, linked to the perspectives of Local Productive Systems (SPS's), proposes as means of agribusiness, the creation of communitarian undertaking in the shape of agro industries, in which the local vocation products would receive logistic treatment within a wide process of rationalization of the production. The present paper investigated this model of intervention, focusing on the construction of its methodology within the perspective of promotion of local development, seeking to realize, also, that the perspective of modernization is built from the actions of this program of university extension. Our research used date collected along with the program and its technical collaborators, in the documental investigation (activity report, foment projects, technical articles among others); and in the accompanying of one of its experiences of intervention, the implantation project of the agro industry of Benefiting of Sisal Fiber for production of handcraft material in the county of Cuiuiú, Barra de Santa Rosa - PB. The intervention model identified as communitarian undertaking lies ineffective in the promotion of local development, shocking against the own local productive system of camping tradition and familiar organization. The focus of the model in the rationalization of productive and social structures ends up not considering the environmental question, limiting the project to development to economic nature questions.

Made available in DSpace on 2014-12-17T15:03:28Z (GMT). No. of bitstreams: 1 PauloCMA_DISSERT.pdf: 4872324 bytes, checksum: c2fbbe9b5d2839b7409ecae2d848efcd (MD5) Previous issue date: 2011-12-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The reality of water resources management in semiarid regions, such as the Serid? region, has been shaped by a complex chain involving social-cultural, political, economic and environmental aspects, covering different spheres of activity - from local to federal. Because water is a scarce element, the most rational way pointed out by our recent history has been to move towards an increasing emphasis on the need for a truly rational, integrated, sustainable and participatory water resources management, supported by legislation and by a network of institutions that could materialize it. In this sense, despite all the advances in the formulation of public policies in water resources, which ones have indeed lead to significant changes that have occurred or are underway in semiarid regions such as Serid?? What factors may be preventing the realization of the desires rationality embedded in the framers of water policies intents? How to properly manage water resources if the current actors who promote their management and the political, human, cultural and institutional processes that intervene in this management, show strong traces of unsustainability? The research methodology adopted in this paper led to a breakdown of the traditional approach to water resource management, to integrate it into other areas of knowledge, especially to political science and public administration, catalyzed by the concept of "sustainable development". From a broad, interdisciplinary literature review, an exhaustive characterization of the river basin Serid?, a set of interviews with key people in the public administration acting in the region, a series of diagnoses and a set of propositions were made in order to correct the direction of current public policies for the region. From the point of view of public policies, it is in the deployment phase, not in its formulation, which lies a major problem of the lack of significant progress in water management. The lack of coordination between government programs are well characterized, as well as the lack of efficiency and effectiveness of their actions. The causes of this secular model are also discussed, including political factors and social relations of production, which led to a stalemate difficult, but of possible solution. It can be perceived there is a scenario of progressive deterioration of natural resources of the fragile ecosystem and a network of environmental and social consequences difficult to reverse, the result of a persistent and inertial sociopolitical culture, whose main factors reinforce itself. The work leads towards a characterization of the water resources management also from the perspective of environmental, institutional, political and human sustainability , the latter being identified, particularly as investment in the development of people as autonomous beings - not based in ideological directives of any kind - in the emancipation of the traditional figure of the poor man of the hinterland" to the "catalyst for change" responsible for their own decisions or omissions, based upon an education for free-thinking that brings each one as co-responsible epicenter of (self-) sustainable changes in their midst / A realidade da gest?o dos recursos h?dricos em regi?es semi?ridas, como ? o caso da regi?o do Serid?, tem sido moldada por uma cadeia complexa envolvendo aspectos socioculturais, pol?ticos, econ?micos e ambientais, abrangendo diferentes esferas de atua??o do local ao federativo. Sendo a ?gua um elemento escasso, o caminho mais racional apontado pela nossa hist?ria recente tem sido o de caminhar no sentido de uma ?nfase cada vez maior na necessidade de uma gest?o verdadeiramente racional, integrada, sustent?vel e participativa dos recursos h?dricos, sustentada por uma legisla??o e por uma rede de institui??es que dessem materialidade a essa gest?o. Nesse sentido, apesar de todos os avan?os na parte de formula??o das pol?ticas p?blicas em recursos h?dricos, quais t?m sido, de fato, as mudan?as significativas que j? ocorreram ou est?o em marcha em regi?es semi?ridas como o Serid?? Quais fatores podem estar impedindo a realiza??o da desejada racionalidade embutida na inten??o dos formuladores das pol?ticas h?dricas? Como gerir adequadamente recursos h?dricos, sendo que os atuais atores que promovem a sua gest?o, os processos pol?ticos, humanos, culturais e institucionais que nesta gest?o interv?m, apresentam fortes tra?os de insustentabilidade? A metodologia de investiga??o adotada nesta disserta??o levou a uma ruptura da tradicional abordagem da gest?o de recursos h?dricos, para integr?-la a outras ?reas do conhecimento, notadamente ?s ci?ncias pol?ticas e ? administra??o p?blica, tendo como elemento agregador o conceito de desenvolvimento sustent?vel . A partir de uma ampla e interdisciplinar an?lise bibliogr?fica, de uma caracteriza??o exaustiva da bacia do rio Serid? e de um conjunto de entrevistas com pessoas-chave da administra??o p?blica atuantes na regi?o, chegou-se a uma s?rie de diagn?sticos e um conjunto de proposi??es para a corre??o de rumos das atuais pol?ticas p?blicas para a regi?o. Sob o ponto de vista das pol?ticas p?blicas, ? na fase de implanta??o, e n?o na de sua formula??o, que reside um dos principais problemas da falta de avan?o consider?vel na gest?o h?drica. A falta de articula??o entre programas governamentais est?o bem caracterizadas, bem como a falta de efici?ncia, efetividade e efic?cia de suas a??es. As causas desse modelo secular s?o tamb?m discutidas, abrangendo fatores pol?ticos e as rela??es sociais e de produ??o, que levaram a um impasse de dif?cil, mas poss?vel solu??o. Como pano de fundo, observa-se um cen?rio de progressiva deteriora??o dos recursos naturais do fr?gil ecossistema e uma rede de consequ?ncias ambientais e sociais dif?ceis de serem revertidas, fruto de uma cultura sociopol?tica persistente e inercial, cujos fatores principais refor?am a si mesma. O trabalho conduz no sentido de uma caracteriza??o da gest?o de recursos h?dricos tamb?m pelo vi?s da sustentabilidade ambiental, institucional, pol?tica e humana, sendo esta ?ltima identificada, sobretudo, como investimento no desenvolvimento das pessoas enquanto seres aut?nomos e n?o no seu adestramento ideol?gico de qualquer natureza -, na emancipa??o da figura tradicional do pobre sertanejo para o agente catalisador de mudan?as respons?vel por suas decis?es ou omiss?es, tendo como fundamento uma educa??o para o livre-pensar que coloque o indiv?duo como epicentro co-respons?vel das mudan?as (auto)sustent?veis em seu meio

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From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / A stochastic model is presented for the prediction of sediment yield in a semi-arid watershed based on rainfall data and watershed characteristics. Random variables which lead to uncertainty in the model are rainfall amount, storm duration, runoff, and peak flow. Soil conservation service formulas are used to compute the runoff and peak flow components of the universal soil loss equation, and a transformation of random variables is used to obtain the distribution function of sediment yield from the joint distribution of rainfall amount and storm duration. Applications of the model are in the planning of reservoirs and dams where the effective lifetime of the facility may be evaluated in terms of storage capacity as well as the effects of land management of the watershed. In order to calibrate the model and to evaluate the uncertainties involved, experimental data from the Atterbury watershed near Tucson, Arizona were used.