Dear Friend,

While climate change affects surface water resources directly through changes in
the major long-term climate variables such as air temperature, precipitation,
and evapotranspiration, the relationship between the changing climate variables
and groundwater is more complicated and poorly understood. The greater
variability in rainfall could mean more frequent and prolonged periods of high
or low groundwater levels, and saline intrusion in coastal aquifers due to sea
level rise.

Groundwater resources are related to climate change through the direct
interaction with surface water resources, such as lakes and rivers, and
indirectly through the recharge process. The direct effect of climate change on
groundwater resources depends upon the change in the volume and distribution of
groundwater recharge. Therefore, quantifying the impact of climate change on
groundwater resources requires not only reliable forecasting of changes in the
major climatic variables, but also accurate estimation of groundwater recharge.
Quantification of the groundwater recharge will help in taking appropriate
adaptation strategies due to the impact of climate change.

There have been many studies relating the effect of climate changes on surface
water bodies. However, very little research exists on the potential effects of
climate change on groundwater. The scientific understanding of an aquifer's
response to climate change has been studied in several locations within the past
decade. These studies link atmospheric models to unsaturated soil models (such
as Visual HELP), which were further linked into a groundwater model (Modflow).
The groundwater models used were calibrated to current groundwater conditions
and stressed under different predicted climate change scenarios. The
HELP-MODFLOW approach proceeds in the following manner -

1. Synthetic generation of daily values of precipitation, mean temperature, and
solar radiation (using a weather generator) for projected climate change.

2. Estimation of groundwater recharge based on available precipitation and
temperature records and anticipated changes to these parameters (using Visual
HELP).

3. Quantification of the spatially distributed recharge rates using the climate
data and spatial soil survey data.

4. Simulation of groundwater flow using each recharge data set and evaluation of
the changes in groundwater flow and levels through time.

Regarding the above approach, I would like to know the views of learned members
on the following aspects -

(a) Which is the most appropriate method to downscale GCM outputs for a basin?

(b) If there are any flaws associated with HELP-MODFLOW methodology (described
above) mostly used by various researchers during last few years?

(c) If the runoff generation process (rainfall-runoff modelling) needs to be
essentially incorporated in the study?

(d) Whether instead of HELP, distributed unsaturated modelling (Richards
equation) should be done for climatic impact studies? What are the relative
advantages of using HELP (e.g. simplistic approach and ease of use) and
disadvantages of distributed modelling (e.g. extensive data requirement and
large computation resources) and vice versa?

(e) Whether any comprehensive overland-unsaturated-saturated model such as
MIKE-SHE can be used for studying the impact of climate change on groundwater
recharge? And relative advantages and disadvantages?

I look forward for the comments on above.

Regards
Kumar
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C. P. KUMAR
Scientist 'E1'
National Institute of Hydrology
Jal Vigyan Bhawan
Roorkee - 247667 (Uttarakhand)
INDIA

Web Page : http://www.angelfire.com/nh/cpkumar/
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