http://dx.doi.org/10.1080/07055900.2013.808167

We analyzed this for the Central Valley of California for the A2 scenario using a watershed precipitation-runoff model combined with our integrated hydrologic model MODLOW-OWHM. This approach allows the analysis of volumes but also rates of use and movement of water and secondary effects such as loss of streamflow and land subsidence.

Hanson, R.T., Flint, L.E., Flint, A.L., Dettinger, M.D., Faunt, C.C., Cayan, D., and, Schmid, Wolfgang, 2012, A method for physically based model analysis of conjunctive use in response to potential climate changes: Water Resources Research, Vol. 48, 23p., doi:10.1029/2011WR010774

Hope this is of interest.

Thank you so much for your sharing Randall. It seems like the USGS softwares have open-source codes available free-of-charge. Am I right? 

Yes that is correct

This is a wonderful question. Climate variability can be analyzed based on a long term measureed climate variables that indicate the variable trends in specially precipitation. The future projection of climate change is a key step to analyze future impact of climate change on hydrology and water resources. Analyzing the future climate change impact on water resources involves downscaling of several GCM into watershed level climate variables and using echohdrological modes to predict its impact on the different components of hydrological cycle.

Let my attempt the Aspects/Issues 1 by 1.

1. Decreasing trend of inflow is observed in most of Iran's main rivers.

Ans: This can be due to anthropogenic (deforestation, dam building, diversion, consumption, retention etc to name a few) as well as temperature rise (causing excessive evapo-transpiration). Outflow being a function of inflow, if the later changes the former varies. Inflow in these rivers are from precipitation and also base flow (at least temporarily). Again inflow is a function of regional forest cover. I feel that there has been long-term land use change in the catchment. You may analyse Satellite Imagery for the purpose.

2. Analysing decreasing trend of river' inflows

Ans: This can be computed/done with the help of a locally developed model and then calibrating it against catchment parameters. In specific the hydrologic budget equation for the areas/watersheds of concern must be prepared for long term analysis.

The undersigned is working on developing a "Theory of Catchment Immunity" to predict the health of a Catchment and the various ecological services it renders not only to human beings but also to others of an ecological unit/family. In due course of time this may be useful for analysing such situations. You may feel free to contact me for the purpose.

Thanks,

Prof. (Dr.) Arnab Sarma, M.ASCE.

Assam Kaziranga University

Arnab,

There have been a number of water schemes developing in recent years in most watersheds facing decreasing trends in inflows. Therefore, undoubtedly, landuse change as an underlying driving force has had a significant role. However, for a period of time, let's say for example over the last 30 years, which factors have had the most significant impact on the decreasing trend of inflows? How much (by percentage) is the contribution of climate variability, climate change and water consumption individually?

Has climate variability had any impact at all? If yes, could it be concluded that interannual/interdecadal variabilities will have more a significant contribution than climate change in the near future (assuming that there will be ongoing declining trends based on climate change projections and watershed simulations)? Moreover, how much is the contribution of the increasing upstream water consumption compared to climate change and variability?

I agree with your hypothesis....climate variability may well trump climate change in the near term interdecadal time frame....but as Voorsmarty showed n his article in Nature the combination of Climate change and urbanization (or in this context additional development of any kind) will threaten the sustainability of the resources more and more quickly. When surface water is not available then other sources will be sought after such as groundwater. And then the conflicts begin over use and ownership of the water in many settings.

A good question. It is important to differentiate the impact of climate variability and climate change in decadal to multi-decadal time scales. In many cases, the decline of runoff might have resulted from both, and human activites. In my opion, we can not detect any signal of climate change in the lonf-term precipitation series for many river basins at present, and the observed trends, if any, might mostly be caused by climatic variability on the decadal and multi-decadal  time sacles, and the recent human consumptions.

This's very interesting topics to discuss a detecting climate change in watershed scale cause water supply. Finer resolution of climate model, better analysis of surface change in both impact to runoff. But dificulties are in different time scale impact of surface change and climate change.....any comment about this?