Climate change impacts on streamflow,water quality,and best management practices for the Shell and Logan Creek Watersheds in Nebraska,USA

Improvements in the management of water,sediment,and nutrients under future climatic conditions are needed to ensure increased crop and livestock production to meet greater global needs and the future availability of water for competing demands and protection against adverse water quality impairments.This study determined the impacts of future climate change scenarios on streamflow,water quality,and best management practices(BMPs)for two watersheds in Nebraska,USA.The Soil and Water Assessment Tool(SWAT)was employed to simulate streamflow,sediment,total nitrogen(N)and total phosphorus(P)from the Shell Creek Watershed near Columbus,Nebraska and the Logan Creek Watershed near Sioux City,Iowa.Available streamflow and water quality records for the two watersheds were used to calibrate model parameters that govern streamflow,sediment,and nutrient responses in SWAT.For each watershed,precipitation,air temperature,and CO2 concentrations were input to SWAT for four climatic conditions:a baseline condition for the 1980 to 2000 period and the SRES A2,A1B,and B1 climate scenarios for a future period from 2040 to 2059.Findings from this study suggest that under the three future climate change scenarios,sediment losses are expected to be about 1.2 to 1.5 times greater than the baseline condition for Shell Creek and 2 to 2.5 times greater for Logan Creek;total N losses are expected to be about 1.2 to 1.4 times greater for Shell Creek and 1.7 to 1.9 times greater for Logan Creek.Relative to the baseline,total P losses under the future climate scenarios are projected to be about the same for Shell Creek and 1.5 to 1.7 times greater for Logan Creek.Findings from this study also suggest that future projected increases in both precipitation and CO2 concentration account for net increases in streamflow,but in different ways on each watershed.

Comparison of three regionalization techniques for predicting streamflow in ungaged watersheds in Nebraska,USA using SWAT model

This study compared three approaches,regional averaging,nearest neighbor,and donor techniques,to regionalize parameters in the Soil and Water Assessment Tool(SWAT)on eleven watersheds located in the Dissected Plains,Plains,and Rolling Hills Landforms in the eastern portion of the State of Nebraska,USA.Within the Rolling Hills Landform,three watersheds were randomly selected as calibration watersheds while two were randomly selected as validation watersheds.Two watersheds were randomly selected as calibration watersheds while one was randomly selected as a validation watershed within each of the Dissected Plains and Plains Landforms.The seven calibration watersheds were used to provide the necessary calibrated parameter sets to execute each of the regional approaches,while the four validation watersheds were used to assess the impact of applying each of these approaches to an uncalibrated watershed.Percent Bias(PBIAS)and the Nash Sutcliffe Coefficient of Efficiency(NSE)were used to assess model performance.Test results of this study show that all three methods performed poorly,since the majority of watersheds among each method tested exhibited PBIAS values greater than ±25% and/or NSE values less than 0.50,which were considered to be unsatisfactory in terms of model performance.The average regionalization,nearest neighbor and donor methods resulted in only four(two calibration and two validation),zero and one satisfactory set of simulated watershed results,respectively.The findings from this study indicate that although each watershed was successfully calibrated with NSE values ranging from 0.51 to 0.84,none of the three regionalization methods provided suitable calibration data sets to define parameter values for performing satisfactory simulations on ungaged watersheds across the eastern Nebraska landscape.