HR: 16:20h
AN: B34A-01 INVITED     [Abstracts]
TI: Long-Term Trends in River Flow From Semiarid Rangelands: Degradation and Recovery
AU: * Wilcox, B P
EM: bwilcox@tamu.edu
AF: Ecosystem Science and Management, Texas A&M University, College Station, TX 77803, United States
AU: Huang, Y
EM: yunh@tamu.edu
AF: Ecosystem Science and Management, Texas A&M University, College Station, TX 77803, United States
AU: Narasimhan, B
EM: balaji@neo.tamu.edu
AF: Ecosystem Science and Management, Texas A&M University, College Station, TX 77803, United States
AB: In the last 100 years or so, desertification, degradation, and woody plant encroachment have altered huge tracts of semiarid rangelands. It is expected that the changes thus brought about significantly affect water balance in these regions; and in fact, at the headwater-catchment and smaller scales, such effects are reasonably well documented. For larger scales, however, there is surprisingly little documentation of hydrological change. In this paper, we evaluate the extent to which streamflow from large watersheds in central Texas has changed concurrent with the dramatic shifts in vegetation cover (conversion from grasslands to woodlands) that have taken place during the last century. Our study focused on the three watersheds that supply the major tributaries of the Concho River—those of the North Concho (3279 km2), the Middle Concho (5398 km2), and the South Concho (1070 km2). Using data from the period of record (1926-2005), we found that annual streamflow for the North Concho decreased by about 70% between 1960 and 2005. Not only did we find no downtrend in precipitation that might explain this reduced flow, we found no corresponding change in annual streamflow for the other two basins. When we analyzed trends in baseflow and stormflow separately, however, we found that in spite of large increases in mesquite and juniper cover, baseflow for all the watersheds has remained essentially consistent since 1960 (and may even have increased). At the same time, stormflows (floods) were fewer and of smaller magnitude. In other words, the same amount of precipitation, on average, generated less stormflow after 1960 than before. We suggest that these lower stormflows result from generally higher soil infiltrability due to the greater density of both woody and herbaceous plants. There is no indication that the decline in streamflow is related to diminished baseflows caused by extraction of subsurface water by woody plants.
DE: 0483 Riparian systems (0744, 1856)
DE: 1813 Eco-hydrology
DE: 1860 Streamflow
SC: Biogeosciences [B]
MN: 2007 Joint Assembly