“As-If” the Climate Has Changed; What We Can Expect in Hydrologic Response

Abstract:

Predicting the effects of climate change through hydrologic modeling with hydrologic forcing representative of historic and future climates. Understanding the hydrologic impacts of various climate scenarios and pathways is accomplished with a physics-based distributed hydrologic model with historic and future precipitation and evapotranspiration inputs. Vflo is a gridded hydrologic model setup for the 71,009 sq.-km. study area, the Canadian River, extending from arid areas in eastern New Mexico, across the Texas Panhandle to Lake Eufaula in sub-humid eastern Oklahoma. This model uses merged radar and rain gauge data to generate hydrographs at gauged and ungauged locations. Vflo is calibrated to observed stream gauge data minimizing Nash-Sutcliffe error function for volume and discharge. Streamflow characteristics at ungauged locations, for both historic and future scenarios, are used to develop ecological relationships between water quality, discharge, and fish species.

Testing the change in hydrologic response from future potential evapotranspiration (PET) and future precipitation is accomplished using observed rainfall. Historical rainfall is perturbed to represent future climate scenarios. Model-based simulations are used to test various scenarios comprising: 1) warmer and drier, 2) warmer and status quo precipitation, and 3) status quo PET but drier. Bias corrected and spatially down-sampled CMIP3 datasets are used to create perturbations for the latter portion of the 21^st Century, 2070-2099. The change in precipitation and PET between 1970-1999 and 2070-2099 is applied to radar data from the observed period, 1995-2010. Then GCM-predicted changes in precipitation under the perturbation of historic rainfall accomplishes an important feature, i.e. preserving realistic spatial, temporal, and convective patterns of rainfall typical of the southern plains, which adds confidence to the model-based simulation of future climate impacts. Simulation of the perturbed climate scenarios reveals the system to be precipitation limited, resulting in less sensitivity to warmer conditions and associated increases in PET, compared with more sensitivity to drier precipitation regimes as seen in the figure below showing runoff climatology.