Characterizing Drought Behavior using Unsupervised Machine Learning for
Improved Understanding of Future Drought in the Colorado River Basin
Abstract
Drought is a pressing issue for the Colorado River Basin (CRB) due to
the social and economic value of water resources in the region and the
significant uncertainty of future drought under climate change. Here, we
use climate simulations from various Earth System Models (ESMs) to force
the Variable Infiltration Capacity (VIC) hydrologic model and project
multiple drought indicators for the sub-watersheds within the CRB. We
apply an unsupervised machine learning (ML) based on Non-Negative Matrix
Factorization using K-means clustering (NMFk) to synthesize the
simulated historical, future, and change in drought indicators within
the sub-watersheds. The unsupervised ML approach can identify
sub-watersheds where key changes to drought indicator behavior occur,
including shifts in snowpack, snowmelt timing, precipitation, and
evapotranspiration. While changes in future precipitation vary across
ESMs, the results indicate that the Upper CRB will experience increasing
evaporative demand and surface-water scarcity, with some locations
experiencing a shift from a radiation-limited to a water-limited
evaporation regime in the summer. Large shifts in peak streamflow are
observed in snowmelt-dominant sub-watersheds, with complete
disappearance of the snowmelt signal for some sub-watersheds. Overall,
results indicate a concerning increase in drought risk. The work
demonstrates the utility of the NMFk algorithm to efficiently identify
behavioral changes of drought indicators across space and time. Our
unsupervised ML approach can be applied to other spatiotemporal data to
process and understand vast arrays of data associated with climate
impacts analysis of hydrologic change, assisting planners to rapidly
assess potential risks associated with extreme events.