Climate warming impacts on the seasonality of irrigation demand help to alleviate warming-induced reductions in summer water availability
Abstract
Basins with winter-dominant precipitation rely on snowpack storage to meet irrigation needs in the summer. These basins are susceptible to warming-induced snowpack depletion and earlier snowmelt, causing the hydrograph to peak earlier in the year. However, shifting water supply is only half the story. How warming impacts irrigation water demand seasonality is just as important for understanding future water scarcity. In this work we use the coupled hydrologic and cropping systems model, VIC-CropSyst, to investigate 1) how water supply and irrigation demands are projected to shift across the Columbia River Basin (CRB), a snowmelt-dominant basin located in the US Pacific Northwest, over the first half of the 21st century, 2) what variables control these shifts, and 3) the implications of the relative shifts in water supply and demand for water scarcity in eastern Washington State. Our results indicate that supply shift is significantly affected by mean winter temperature, which controls how much of the annual streamflow is derived from snowmelt. Since snowmelt-dominant watersheds along the Eastern slope of the Cascades are already affected by warm weather, further warming may greatly decrease the snowmelt contribution to streamflow. Early results also indicate that watershed aridity is the key climatic factor influencing shifts in irrigation demand timing and that crop mix is an important management factor. More arid watersheds experience earlier demand shift as the dry season gets even drier and early-season irrigation demands increase. The phenological response of crops to climate change varies widely by crop type. The key characteristics for determining demand timing include the canopy growth curve vs. growing degree days and the length of the growing season. Crops that accumulate leaf area more quickly require more water early on, shifting peak demand closer to peak streamflow and thereby helping to alleviate water scarcity. In contrast, perennial crops like fruits or crops that are clipped multiple times need water over a longer period, thereby widening the gap in timing between supply and demand. The difference between supply and demand centers of timing is an indicator of vulnerability because the greater the disparity, the greater the potential for water right curtailments and low environmental flows.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H44F..04Y