Comment on “Climate and agricultural land use change impacts on streamflow in the upper midwestern United States,” by Satish C. Gupta et al.

Abstract

The paper ''Climate and agricultural land use change impacts on streamflow in the upper midwestern United States'' by Satish C. Gupta, Andrew C. Kessler, Melinda K. Brown, and Francis Zvomuya (hereafter referred to as Gupta et al.) purports to evaluate ''the relative importance of changes in precipitation and LULC (land use, land cover) on streamflow in 29 Hydrologic Unit Code 008 watersheds in the Upper Midwestern United States.'' However, as we report here, the approach used by Gupta et al. is wholly inadequate for making such an evaluation. Gupta et al. use strong language to criticize other studies and imply a level of certainty that goes well beyond, and in some cases is entirely unsupported by, the results they have presented. We take this opportunity to point out several critical flaws in their study.

Reply to comment by Belmont et al. on “Climate and agricultural land use change impacts on streamflow in the upper midwestern United States”

“…Finally, we disagree with Belmont et al [2016] and several others who have used changes in soybean acreage as a surrogate of LULC changes in regression or other analyses. Before one uses soybean acreage, other crop area, or some other variable as a surrogate in streamflow analysis, one must address the question: How does this surrogate variable relate to other factors under the broad umbrella of LULC change (cropping system, extent of tile drainage, crop varieties, stage of crop growth, etc.)…”

“…In that case, the starting date is not that important. In terms of number of years (B|A for the LeSueur and the Blue Earth River gages), our values are slightly different than Belmont et al [2016]. For example, for the LeSueur River gage our B|A values were 34|31 for the period 1940-2009.…”

“…With respect to Belmont et al [2016] comments ''Most of Gupta et al's conclusions rely on analysis of annual streamflow and precipitation data. The annual timescale obscures .…”

“…That is also the case for watersheds and time periods that Belmont et al [2016] has listed in their Table 1. We have included similar 5 year moving average plots both with 1975 and 1990 (as suggested by Belmont et al [2016]) as breakpoints for the Whetstone River watershed (gage 5 05291000) in Figure S2. There was no effect of the breakpoint on 5 year moving average trends.…”

“…If there was no value given for a month, the data for that year was not included. We have also contacted USGS about the daily missing values in 1930s that Belmont et al [2016] mentioned for the Whetstone River watershed (USGS 05291000). USGS recompiled the data in 1950 and they estimated the discharge for the missing days (mostly winter days) in monthly time steps.…”