Two catchments of diverse hydrologic character were chosen in which to test the hypothesis that tree-ring indices contain information about runoff that is of pertinent interest to the hydrologist. These two catchments, Bright Angel Creek basin in extreme north-central Arizona and Upper San Francisco River basin in extreme east-central Arizona and west-central New Mexico, are situated in different climatic regions. Although two semiannual maxima, summer and winter, occur in the annual precipitation regime, at Bright Angel Creek the winter maximum is dominant, resulting in large amounts of snow accumulation, and at Upper San Francisco River the summer maximum is dominant. These contrasting precipitation regimes in association with the annual temperature regimes create climatic conditions for which the growth response of the trees, specifically Douglas fir, the species used in the study, and the precipitation-runoff response are greatly different and comparably complex. The complexity of the climate-growth, climate-runoff relationships necessitated the use of multivariate methods in assessing their similarities and dissimilarities. The technique used here is that of principal components, with physical meaning attached to the components by comparison with the results of other statistical approaches such as autocorrelation, cross correlation, autospectra, and cross spectra, and such tree-ring statistics as the coefficient of -mean sensitivity. The orthogonality property of the principal components was used to develop prediction equations with a minimum of variables through use of multiple linear regression. The general approach was to relate ring-width indices to climate and develop a response function, to relate runoff to climatic variables and develop a response function, and finally to develop a prediction equation for predicting runoff from ring-width indices. Prediction equations and 214-year (1753-1966) synthetic runoff series were developed for both basins. The results for Bright Angel Creek basin are not impressive because the best prediction equation accounts for only 51% of the year-to-year variance in the annual runoff. However, this was not wholly unexpected, as it is shown that the nature of the annual runoff regime and the statistical nature of the ring-width index series from this basin are not conducive to maximum hydrologic information. Nevertheless, it is shown that an improved estimate of the mean annual runoff can be gained from the synthetic series. For Upper San Francisco River basin the results were more satisfactory: 72% to 79% of the annual variance in runoff can be accounted for using prediction equations based on ring-width indices, where one equation uses untransformed values of runoff (72%) and the other uses log-transformed values of runoff (79%). The synthetic series shows an improved estimate for the mean annual runoff but also offers the hydrologist a valuable tool in providing a series from which useful information can be obtained that could be valuable in decision-making processes concerning reservoir design and operation.

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The purpose of this research was to: (1) reconstruct climate for the malpais region from long-lived trees and remnant wood; (2) reconstruct the fire history of forests in the malpais; and (3) investigate short-term and long-term relationships between wildfire and climate. To reconstruct climate, I calibrated a 2,129 year long tree-ring chronology (136 BC - AD 1992) with annual rainfall (previous July to current July). Since AD 100, seven major long-term trends in rainfall occurred. Above normal rainfall occurred during AD 81-257, 521-660, 1024-1398 and 179 1- 1992, while below normal rainfall occurred during AD 258-520, 661-1023 and 1399- 1790. The prolonged drought from AD 258-520 was unsurpassed in its intensity, while rainfall during the most recent 200 years has exceeded any since AD 660. The reconstruction of long-term climate trends confirmed the general sequence of environmental change over the last 2,000 years for the southern Colorado Plateau. To reconstruct past fire occurrences, 217 fire-scarred trees were collected from nine sites representing the major habitat types of the malpais and dendrochronologically dated. Fire frequency was highest at sites on cinder cones and on the highly-weathered basalt flows (ca. once every five years), and lowest on the isolated kipukas and on the Hoya de Cibola Lava Flow (once every 10-12 years). Fire frequency decreased along a north to south gradient, reflecting changing vegetation properties. Combined information revealed fire occurred once every two years, while more widespread fires occurred once every 2.5 years. Fires were largely asynchronous between sites, suggesting the malpais landscape effectively hinders fire spread. Past fire history at El Malpais was characterized by four temporally distinct periods: (1) FH-1 (prior to 1782): high fire frequency, patchy fires, throughout the growing season; (2) FH-2 (1795 - 1880): longer fire intervals, widespread fires, mostly early season fires; (3) FH-3 (1893 - 1939): even longer intervals, decreased widespread fires; (4) FH-4 (1940 - 1992): longest fire-free periods during the last 600 years. The increase in rainfall and the simultaneous change in fire regimes ca. 1790 was likely related to an increase in summer monsoonal rainfall due to changes in hemispheric circulation patterns. The decrease in fire spread ca. 1880 was most likely due to intense sheep grazing, while the change ca. 1940 reflects greater efficiency in fire suppression techniques. The presettlement fire regime emphasizes that the current absence of fire in the monument exceeds the historical range of variability established for the presettlement period. Unless effects of past humanrelated disturbances are mitigated, fire regimes of El Malpais will continue to favor high-intensity, catastrophic fires.

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