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The Western Cape (South Africa) recently witnessed the most severe drought on record. The meteorological drought, which was characterised by below-normal rainfall for three consecutive years (2015 – 2017), cascaded to agricultural and then hydrological drought, resulting in devastating socio-economic consequences. While some studies indicate that climate change may increase the severity and frequency of droughts in the Western Cape in the future, there is a lack of information on how to mitigate the effects of future climate change on hydrological drought. This dissertation therefore investigated the extent to which land-use changes could be applied to reduce climate change impacts on future hydrological drought in this region. For the study, the revised Soil Water Assessment Tool (SWAT+) was calibrated and evaluated over four river basins in the Western Cape, and the climate simulation dataset from the COordinated Regional Downscaling EXperiment (CORDEX) was bias-corrected. Using the bias-corrected climate data as a forcing, the SWAT+ was used to project the impacts of future climate change on water yield and hydrological drought in the four basins and to quantify the sensitivity of the projection to four feasible land-use change scenarios in these basins. The relevant land-use scenarios are the expansion of mixed forests (FrLand), the restoration of grassland (GrLand), the restoration of shrubland (SrLand), and the expansion of cropland (CrLand). The model evaluation shows good agreement between the simulated and observed monthly streamflow at hydrological stations, and the bias correction of the CORDEX datasets improved the quality of the SWAT+ hydrological simulations in the four basins. The climate change projection depicts an increase in temperature and potential evapotranspiration but a decrease in precipitation and all the hydrological variables. Drying is projected across the Western Cape, and the magnitude of such drying increases with higher global warming levels (GWLs). The land-use changes alter the impacts of climate change by influencing the hydrological balance. While FrLand mitigates the impacts of climate change on the frequency of hydrological drought by increasing streamflow, soil water and percolation, CrLand mitigates the impacts by increasing surface runoff. However, the magnitudes of these land-use change impacts are very small compared to the climate change impacts. Hence, the results suggest that land-use changes may not be an efficient strategy for mitigating the climate change impacts on hydrological drought over the region. The findings obtained from this 2 research provide relevant information towards mitigating the severity of future droughts and improving water security in Western Cape River Basins.

Mountain meadows in the western USA are experiencing increased rates of conifer encroachment due to climate change and land management practices. Past research has focused on conifer removal as a meadow restoration strategy, but there has been limited work on conifer transpiration in a pre-restoration state. Meadow restoration by conifer removal has the primary goal of recovering sufficient growing season soil moisture necessary for endemic, herbaceous meadow vegetation. Therefore, conifer water use represents an important hydrologic output toward evaluating the efficacy of this active management approach. This study quantified and evaluated transpiration of encroached conifers in a mountain meadow using sap flow prior to restoration by tree removal. We report results of lodgepole pine transpiration estimates for an approximate 1-year period and an evaluation of key environmental variables influencing water use during a dry growing season. The study was conducted at Rock Creek Meadow (RCM) in the southern Cascade Range near Chester, CA, USA. Sap flow data were collected in a sample of lodgepole pine and scaled on a per-plot basis to the larger meadow using tree survey data within a stratified random sampling design (simple scaling). These estimates were compared to a MODIS evapotranspiration (ET) estimate for the meadow. The 1-year period for transpiration estimates overlapped each of the 2019 and 2020 growing seasons partially. The response of lodgepole pine transpiration to solar radiation, air temperature, vapor pressure deficit, and volumetric soil water content was investigated by calibrating a modified Jarvis-Stewart (MJS) model to hourly sap flow data collected during the 2020 growing season, which experienced below average antecedent winter precipitation. The model was validated using spatially different sap flow data in the meadow from the 2021 growing season, also part of a dry year. Calibration and validation were completed using a MCMC approach via the DREAM(ZS) algorithm and a generalized likelihood (GL) function, enabling model parameter and total uncertainty assessment. We also used the model to inform transpiration scaling for the calibration period in select plots in the meadow, which allowed comparison with simple scaling transpiration estimates. Average total lodgepole pine transpiration at RCM was estimated between 220.57 ± 25.28 and 393.39 ± 45.65 mm for the entire campaign (mid-July 2019 to mid-August 2020) and between 100.22 ± 11.49 and 178.75 ± 20.74 mm for the 2020 partial growing season (April to mid-August). The magnitude and seasonal timing were similar to MODIS ET. The model showed good agreement between observed and predicted sap velocity for the 2020 partial growing season (RMSE = 1.25 cm h-1), with meteorological variables modulating early growing season sap flow and volumetric soil water content decline imposing transpiration decrease in the late growing season. The model validation performed similarly to calibration in terms of performance metrics and the influence of meteorological variables. The consistency of the declining volumetric soil water content effect during the late growing season between periods could not be evaluated due to an abridged validation period. Overall, the implementation GL-DREAM(ZS) showed promise for future use in MJS models. Lastly, the model derived transpiration estimates for the 2020 partial growing season showed some of the potential utility in using the MJS model to scale sap flow at the study locale. It also highlights some of the key limitations of this approach as it is executed in the present study.

Montane meadows provide essential habitat for a variety of unique species and important ecosystem services in the western United States. Although important, meadows have experienced increased rates of conifer encroachment due to climate change, fire suppression and grazing. To combat meadow degradation from conifer encroachment, land managers have employed various restoration strategies one of which is conifer removal. Multiple studies have investigated the relationship between meadow hydrology and vegetation; however, few have assessed the effect of conifer removal on meadow groundwater. The goal of this study is to determine if the removal of conifers from an encroached meadow has an effect on depth to the groundwater table (WTD) and soil moisture content (SMC), and to investigate the accuracy and potential usefulness of evapotranspiration (ET) calculation methodologies for montane meadows. This goal will be accomplished by the subsequent objectives: 1) perform an analysis of WTD and SMC in an encroached meadow preceding and following conifer removal and upland thinning; 2) calculate and compare daily ET estimates in a previously restored meadow using diurnal groundwater table fluctuation, diurnal groundwater fluctuation modelling, and SMC. Miranda Cabin Meadow (MC) is located within the Upper American River Watershed, southeast of French Meadows Reservoir, at an elevation of 6,200 feet. MC received conifer removal, upland thinning and road decommissioning in the fall of 2018 as part of the American River Conservancy’s American River Headwaters Restoration Project. This study found the average WTD in MC during the growing season decreased from 4.91 feet prior to restoration, to 3.39 feet after restoration. In addition, the number of days the WTD was within 0.98 feet and 3 feet increased from 12 days and 34 days, to 31 and 49 days. Analysis of SMC in MC was limited due to gaps in data, however this study found that after restoration the average weekly SMC decreased at a slower rate than prior to restoration, possibly indicating decreased hydrologic output from ET. Based upon WTD during the growing season and the limited SMC data it appears that removal of conifers and upland thinning at MM promotes SMC and WTD conditions conducive to meadow vegetation communities. Marian Meadow (MM), located in Plumas County, CA at an elevation of 4,900 feet, received conifer removal as part of a timber harvest plan carried out by Collins Pine Company in July 2015. The soil moisture sensors used in this study were installed in MM in September 2013 for previous graduate thesis research. Groundwater table data was collected using 10-foot wells installed in July of 2018. Daily ET was calculated during August 2018 using three methodologies, and during September 2018 using two methodologies. Daily ET estimates calculated using diurnal groundwater table fluctuation and the White method averaged 11.8 mm per day in August and 9.1 mm in September. Using diurnal groundwater table fluctuation modelling this study calculated an average daily ET of 4.2 mm in August and 3 mm in September. Daily ET estimates based on SMC were calculated for August 2018 using two methods which produced estimates of 0.9 mm and 1.2 mm per day. All three methods for calculating ET produced some daily estimates that compare well to previous research of Et in Sierra Nevada meadows, however the White method generally overestimated daily Et while SMC methods underestimated ET. Groundwater table fluctuation modelling produced the best estimates of daily ET for both August and September. ET results in this study support previous research on the applicability of the White method; and they also suggest that the applicability of groundwater fluctuation modelling to estimate meadow daily ET in Sierra Nevada montane meadows be investigated further.

Oil sands mining in Alberta completely transforms the natural boreal landscape of upland forests, wetlands and lakes into open pits, tailings and overburden piles. By law, industry is required to return the landscape to its pre-disturbance land capability. While previous reclamation efforts have mainly focused on upland forest ecosystems, rebuilding wetland systems on soft tailings has only recently become a research focus. The dry, sub-humid climate and high salinity levels of underlying mining material complicate reconstruction of wetlands within this region. In 2012, Syncrude Canada Ltd. completed construction of the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland system to evaluate wetland reclamation strategies. SFW includes an active pumping system, upland hummocks, a fen wetland and underdrains. This study examined the watershed-scale water balance in the first two years after commissioning (2013 and 2014). The first paper presents a semi-distributed water balance approach examining the fluxes and stores of different landscape units. Artificial pumping controlled the water balance in 2013, with approximately double the annual precipitation pumped in and out from May-Oct 2013, causing large water table fluctuations. In 2014, pump management was more passive, and water balance controlled by vertical fluxes. In the second paper, growing season ET rates and controls were assessed using data from three eddy covariance towers in the uplands and lowlands. Average ET rates between uplands and lowlands were similar, with average rates of 2.41 – 2.52 mm d-1. ET was radiatively controlled at all sites. Energy partitioning and ET rates are similar to natural boreal peatlands within the area, however upland areas are expected to increase in ET rates as LAI increases and vegetation matures. This study provides critical quantitative data on the early years of a highly managed watershed. Long-term monitoring is necessary, as water balance dynamics will evolve with vegetation development and climate cycles. / Thesis / Master of Science (MSc)

Climate change is posing a significant threat to terrestrial ecosystems worldwide, in part due to the more frequent occurrence of extreme climatic events such as droughts. While the importance of drought impacts on vegetation has been widely recognized, the time-dependent characteristics of drought-induced response remain insufficiently understood. In this study, we examine the sensitivity of terrestrial evapotranspiration (ET) to water availability in African biomes using a suite of satellite and geospatial data. By correlating a multi-scalar drought index with monthly ET anomalies between 1981 and 2016, the spatiotemporal effects of drought are evaluated and compared against simulations from a coupled vegetation-climate model. The coupling between water availability and ET is found to be largely dependent on aridity conditions and the evapotranspiration regime (energy- vs. soil moisture-limited). We also observed the dominant role of root zone storage capacity in mediating ET response among rainforests and savannas, whereas shrubs and grasslands tend to exhibit much more complex soil-plant interactions. Comparing between model simulations and observations, discrepancies in the magnitude and timing of ET response were evident. Our findings highlight the need for an explicit consideration of plant-available water to improve the representation of hydroclimatic processes in Earth system models.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第24662号 / 農博第2545号 / 新制||農||1098(附属図書館) / 学位論文||R5||N5443(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 小杉 緑子, 教授 北山 兼弘, 教授 北島 薫 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Evapotranspiration (ET) is the sum of the evaporation of water from the Earth’s surface and the total transpiration from plants.  Spatially calculating ET is necessary because it is a major component in quantifying a water budget, and maps provide the spatial ability to display the distribution.  Geographic information systems (GIS) are a powerful and capable tool which can spatially process and integrate equations in order to quantify ET rates.  Probable ET equation types that best fit with ArcMap software were investigated, and the methodology of España et al was evaluated in terms of usefulness and ease of replication, while beneficial areas for future expansion were also commented on.  Interpolation of some weather and other variables, as well as the use of the raster calculator in ArcMap was the basis of the project methodology.  Temperature based ET equations were selected as the best equation category, and then specifically the Blaney-Criddle, Thornthwaite, and Hargreaves equations were used to calculate potential evapotranspiration (PET) rates in British Columbia (BC), Canada. The methodology of España et al provided a relatively easy way to spatially display algebraic evapotranspiration equations.  The results were compared to values of sixteen reference stations, which had been computed by the Penman-Monteith equation.  PET values that were interpolated were not as accurate as hoped, however the Hargreaves and Blaney-Criddle methods produced better results than the Thornthwaite method, which resulted in underestimates.  Nonetheless, the PET distribution pattern was displayed, and of use to show the areas of highest and lowest rates of PET.  In order to produce more accurate values, regional or crop coefficients could be applied to calculate actual evapotranspiration (AET), but time constraints placed on the project restricted the trial of this.

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