A Comparison of Precipitation Downscaling Procedures to Guide Studies of Climate Change Impacts on Flooding and Water Resources

Location: Southwest United States
Sponsors: Department of the Interior, Bureau of Reclamation
PI/Co-PIs: Dr. Eylon Shamir (HRC)
Collaborators: Bureau of Reclamation

In relatively small basins with arid climate, rainfall characteristics are highly variable and streamflow is tightly associated with the nuances of the rainfall temporal and spatial characteristics. Commonly used methods for impact assessment studies of the projected future climate on the local hydrologic conditions were developed and tested mainly in large river basins. However, in recent years, the Bureau of Reclamation (BoR) and other agencies have been engaged in climate impact assessments in smaller river basins and local rural communities. The existing methods and datasets that were developed for larger watersheds may not be adequate for arid ephemeral river basins that are often the prevailing landscape of these rural communities. The objective of this research, which is conducted in two arid watersheds in Arizona (i.e. the Upper Santa Cruz River watershed and the Bill Williams River watershed) are to: 1) evaluate the suitability of various global climate models downscaling methods to produce future projections of precipitation; 2) develop a test to decide on the preferred procedure for a given type of study; and 3) quantify the impact of each method on the BoR planning activities.

As part of this grant, HRC compiled a report that describes the development of the hourly precipitation Weather Generator (WG) for the Upper Santa Cruz River Basin, near the international Mexico-U.S border. This WG was developed as a tool to assess the impact on the water resources of various natural and man-made changes in the basin.  In addition, it was used to explore various water resources management and planning schemes that best address water resources challenges.  (Shamir, E., 2017: Modification and calibration of the rainfall weather generator for the Upper Santa-Cruz River basin, Arizona HRC Technical Note No. 94.  Hydrologic Research Center, San Diego, CA, 1 August 2017.)

An additional HRC report describes the technical details of the hydrologic modeling framework for the Bill Williams River Watershed and Alamo Lake, Arizona.  The primary objective of the  modelling framework, which consists of a precipitation weather generator, a hydrologic model and a lake model for Alamo Lake, is to assess the hydrologic impact of projected climatic changes. (Shamir, E., T. Modrick-Hansen and KP. Georgakakos 2017. Development of hydrologic Modeling Framework for the Bill Williams River Watershed. HRC Technical Note No. 97.  Hydrologic Research Center, San Diego, CA, 1 December 2017. )

This is a collaborative project with Dr. Eve Halper from BoR Phoenix Area Office. The project was funded by the BoR Science and Technology Grant Program under a cooperative agreement between HRC and the BoR Lower Colorado Region (Agreement # R16AC00024).