Temporal variation in water availability

Title	Temporal variation in water availability
Publication Type	Conference Paper
Year of Publication	2004
Authors	Snyder K.A, Tartowski S., Gutschick V.P
Conference Name	Sixth Symposium on the Natural Resources of the Chihuahuan Desert Region
Date Published	October 15, 2004
Conference Location	Alpine, TX
ARIS Log Number	171333
Keywords	Chihuahuan Desert, pulse-driven nature, shifting climate regimes, temporal variation, water availability, weather patterns
Abstract	Desert regions in the southwestern United States and northern Mexico exhibit a high degree of temporal variability in water availability. This temporal variability is a result of shifting climate regimes over centuries and decades, interannual variation in weather patterns, seasonal differences n the nature of winter and summer precipitation, within-season variability of precipitation frequency and magnitude, soil textural properties, differences in vegetation structure, and soil water. Pulses of rainfall during the summer growing season are highly unpredictable and punctuated by intervening dry periods of variable lengths. These dry periods are frequently severe enough to limit biotic activity and modify abiotic processes. Therefore, within a landscape type the relationship between aboveground net primary productivity and annual rainfall lacks predictive power due to the pulse-driven nature of these systems. In the Chihuahuan Desert encroachment of C3 shrub species into areas formerly dominated by C4 grasses appears to interact with water variability and create positive feedbacks that facilitate further shrub encroachment and loss of grass cover. In order to understand these systems, we need to develop knowledge of how temporal patterns in water availability affect ecosystem water use, nutrient availability, productivity, and species composition. Data from rainfall manipulation experiments, Bowen-Ration towers, and long-term soil moisture illustrate that mesquite shrubs respond to both small and large rainfall events, respiratory losses of carbon dioxide often offset photosynthetic uptake of carbon dioxide, and the capacity for carbon sequestration during summer months is largely driven by rainfall patterns.