Impacts of rainfall and air temperature variations due to climate change upon hydrological characteristics: a case study

Authors: QUYANG, YING - Us Forest Service (FS); ZHANG, JIAEN - South China Agricultural University; LI, YIDE - Chinese Academy Of Forestry; PARAJULI, PREM - Chinese Academy Of Sciences; Feng, Gary

Submitted to: Journal of Water and Climate Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2015
Publication Date: 8/31/2015
Citation: Quyang, Y., Zhang, J., Li, Y., Parajuli, P., Feng, G.G. 2015. Impacts of rainfall and air temperature variations due to climate change upon hydrological characteristics: a case study. Journal of Water and Climate Change. p. 1-15. doi: 10.2166/wcc.2015.101.

Interpretive Summary: In this case study, impact of future climate change upon water discharge, evaporation, and outflow in the LYRW, Mississippi was examined using the US EPA’s BASINS-HSPF model. The model was calibrated using a five-year (2000 to 2004) local field and aggregated data and validated using another five-year (2005 to 2010) local field and aggregated data prior to its applications. Very good agreements were obtained between the model predictions and the field observations for model calibration and validation. Four future simulation scenarios were then performed to investigate the water discharge, evaporative loss, and water outflow in response to precipitation and air temperature over a 50-year period from 2001 to 2050. They were CSIROMK35A1B, HADCM3B2, CSIROMK2B2, and MIROC32A1B scenarios. The future climate change data (i.e., air temperature and precipitation) for these four simulation scenarios were obtained from the Rocky Mountain Research Station, USDA Forest Service for LYRW (HUC 08030208). In general, the monthly water discharge, evaporative loss, and outflow varied from year to year as well as from scenario to scenario, which was primarily due to the monthly fluctuations in precipitation. There were very good positive correlations (R2 ranged from 0.82 to 0.91) between the annual mean discharge and the annual precipitation for those four scenarios. The sum, mean, maximum, and minimum values of water discharge, evaporative loss, and water outflow for those four simulation scenarios varied with simulation periods. For a 50-year simulation period, the sum and mean water discharges were in the following order: CSIROMK35A1B > HADCM3B2 > MIROC32A1B > CSIROMK2B2, whereas the maximum water discharge was in the following order: CSIROMK35A1B > MIROC32A1B > HADCM3B2 > CSIROMK2B2; the sum and mean water evaporative losses were in the following order: CSIROMK2B2 > HADCM3B2 > CSIROMK35A1B > MIROC32A1B, whereas the maximum evaporative loss was in the following order: CSIROMK2B2 > CSIROMK35A1B > HADCM3B2 > MIROC32A1B; and the sum, mean, and maximum water outflows were in the following order: CSIROMK35A1B > HADCM3B2 > CSIROMK2B2 > MIROC32A1B. We attributed the discrepancies to the highly non-linear and dynamic variations in precipitation for different simulation periods. Comparison of simulation results between the past 10 years (2001 to 2010) and the future 10 years (2011 to 2020) showed that the sum and mean precipitations from the past 10 years to the future 10 years decreased for all of the four simulation scenarios, which had resulted in decreased evaporative loss and water outflow. Our simulations suggested that the total amount of precipitation had profound impacts upon water outflow and evaporative loss in the LYRW. Impact of air temperature on evaporative loss cannot be deduced from this study. This is because evapotranspiration is a complex process, which is governed not only by air temperature but also by precipitation, vegetation, and soil moisture content. A plot of our simulated evaporative loss against air temperature did show good correlations for all of the simulation scenarios. These correlations could be masked by the precipitation. To compare the impact of air temperature on evaporative loss between the past 10 years and the future 10 years, simulations must be performed with changing air temperature, but with the same precipitation for the past and future 10 years. Further study is thus warranted to investigating impact of the percentage changes in future air temperature, precipitation, and forested land upon water discharge, evaporative loss, and water outflow in the LYRW. This could be accomplished by changing one of three input parameters (i.e., air temperature, precipitation, and forested land) while keeping the other two input parameters unchanged for those four simulation scenarios.

Technical Abstract: Rainfall and air temperature variations resulting from climate change are important driving forces to alter hydrologic processes in watershed ecosystems. This study investigated impacts of past and potential future rainfall and air temperature variations upon water discharge, water outflow (from the watershed outlet) and evaporative loss in the Lower Yazoo River Watershed (LYRW), Mississippi, US, using the BASINS-HSPF model. Four future climate change (i.e., rainfall and air temperature change) scenarios, namely the CSIROMK35A1B, HADCM3B2, CSIROMK2B2, and MIROC32A1B scenarios, were used as input data to perform simulations in this study. Results showed that monthly variations of water discharge, evaporation, and outflow were primarily due to the monthly fluctuations of precipitation rather than air temperature. There were very good positive correlations (R2 ranged from 0.82 to 0.91) between the annual mean water discharge and the annual mean precipitation for those four scenarios. Comparison of simulation results between the past decade (2001 to 2010) and the present decade (2011 to 2020) revealed that the sum and mean water outflow and evaporative loss decreased for all of the four simulation scenarios as a result of the precipitation amount decrease. Our study demonstrated that the amount of precipitation had profound impacts upon water outflow and evaporative loss in the LYRW as a result of climate change.