Assessing CMIP5 Model Ability to Reproduce Large-Scale Drivers of Growing Season Drought Across the South-Central U.S. and the Impact of Model Performance on Future Projections
Abstract
Future projections suggest that climate change is likely to affect the frequency and severity of growing season drought across the South Central U.S. Given the importance of surface water resources to the region's agricultural economy and fast-growing urban centers, we assess the ability of CMIP5 models to simulate the large-scale circulation features that drive variability and trends in regional precipitation and drought risk over this region. Then, given recent trends towards weighting future projections based on the models' historical performance, we examine the extent to which model performance affects the direction and magnitude of future change. South-Central precipitation is characterized by a precipitation peak in May and June, a mid-summer dry period in July and August, followed by a second peak in September and October. Of the 22 CMIP5 models with the required variables, 16 models (group A) reproduce this bimodal distribution, while 6 models (group B) have trouble simulating the mid-summer dry period, instead producing an extended wet season. In A models, the timing and amplitude of the mid-summer westward extension of the North Atlantic Subtropical High (NASH) are realistic, while in the B models, although temporal variations and geophysical locations are also reasonable compared to reanalysis, their magnitudes are too weak to suppress mid-summer precipitation. During warm-season droughts, however, both A and B models reproduce the observed tendency towards a stronger NASH that remains over the region through September, and an intensification and northward extension of the GPLLJ. Similarly, future simulations from both A and B models under an increase in global mean temperature from +1 to +3oC show decreases in summer precipitation related to the combined influences of an enhanced NASH and an intensified GPLLJ. These results suggest that projected increases in summer drought risk are based on a robust shift in large-scale circulation patterns similar to those observed in dry years. They also suggest that model ability to simulate large-scale drivers of seasonal precipitation does not appear to correlate with model ability to simulate the influence of long-term trends and inter-annual variability on precipitation over this region: so model weighting is not likely to alter projected trends.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H14E..06H
- Keywords:
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- 1807 Climate impacts;
- HYDROLOGYDE: 1812 Drought;
- HYDROLOGYDE: 1817 Extreme events;
- HYDROLOGYDE: 1833 Hydroclimatology;
- HYDROLOGY