Most hydrologic studies look at changes in watershed response to rainfall, watershed conditions, and some have addressed land use changes such as urbanization and deforestation. I am not sure that many of these studies has explored the indirect and offsite effects of evapotranspiration losses to broader areas, outside of the study watershed. It has been shown that forests in SE USA that forests may have ET of about 20-30 inches. There are so many potential changes within the watershed to deforestation and urbanization, that few if any studies have explored these secondary, but potentially important effects to adjacent landscapes. Years ago, Moshe Cohen (Israel researcher) shared benefits in reforestation of what appeared to be deforested desert to forest, and how rainfall and streamflow benefitted to the area, converting ephemeral to perennial streams. I believe it would take a significant level of landscape deforestation and urbanization to produce these offsite changes, and also dependent on weather patterns, etc. Forests detain and slow the rate of water movement across the landscape, and also add moisture to airscape. Alternately, urbanization increases runoff, reduces ET. I think it may be difficult to find the long term landscape level weather, raingauges and stream gauges to test the theory. Then to apply that specifically to your area of interest would need the benefits of a appropriate weather model, coupled with the watershed modeling that suits your area. The analytical tools we have today may be able to help address your questions. If you have less than 25% to maybe 50% of the landscape in urban or deforested condition, onsite as well as these offsite changes could be more difficult to detect.

Hi William,

Thanks for your response. The scale I'm looking at is large (think Sahel, interior China, interior Amazon), and at this scale there are time series available for precipitation, evaporation, temperature, etc. (for example the NCEP/NCAR reanalysis). What is missing is runoff, and for that I'm looking for timeseries for one or more large rivers (Nile, Niger, Congo, Amazon, Yangtze, etc.).

Kind regards,

Timmo

Annual runoff coefficient in the Cerhovický Stream catchment

a pdf file is attached

Hi Timmo

I am interested in your hypothesis, as I has been working on it during the early 2000's, with the idea to run a RCM with limit conditions taking into account this runoff coefficient change that we observe in Sahel (runoff increase). but we stopped working on this. So it is good if you are interested to move onward on this.

Of course the increase of runoff coefficient takes away from the basin an significant amount of water. I had a slightly different approach than you, i.e. that the soil moisture content reduction would not have an effect on direct rainfall, but surely it can have an impact on the modification of the heat budget at the soil surface : less water to evaporate means less energy used and thus an increase in soil surface temperature ? This could mean an increase of the lower atmosphere air masses instability, which could in turn explain the increase of high energy rainfall event increase since some decades in the Sahel (look also at the Geremy Panthou and Theo Vishel work on Sahel Rainfall changes)

I have some runoff time series, and associated rainfall on river basins in Sahel. We can have a look on this together if you want.

If you want to have a look to my previous works -or those of my former students and colleagues-, please look at my papers in RG. There a re many dealing with this.

Best

Gil

PS a few papers on this topic

Dear Gil,

Awesome, thanks! I'll read the papers and get back to you.

Timmo

Hi Timmo

any results to share ?