The Hindu Business Line : Soil moisture has a role in rainfall: Study

According to preliminary findings of the latest National Aeronautics Space Administration (NASA) research, the other "hot spots" are found in the central plains of North America and equatorial Africa. Less intense hot spots show up in South America, Central Asia and China.

Understanding soil moisture levels and their connection to precipitation have important implications, say researchers. It may improve seasonal forecasting of rainfall vital to water managers, as well as improve the accuracy of short-term weather forecasts. Interest in the study is therefore high at national weather centres, like the National Centres for Environmental Prediction (NCEP) in the US.

According to sources in India Meteorological Department (IMD), the research may, in turn, have implications for those parts of India where the southwest monsoon has performed poorly this year. For instance, hot and dry weather is expected to prevail through the week across much of northwest India and even up to Pakistan. Topsoil moisture is reported to be meagre to very meagre in areas bordering West Rajasthan as well as in Tamil Nadu, Northern Karnataka and most of Andhra Pradesh.

But surplus soil moisture is indicated in the rest of the country, except parts of North Central and North East India, which have experienced heavy precipitation during the ongoing monsoon. Favourable growing conditions have been indicated for most of the croplands, except areas where flooding has posed a problem.

The hot spots are, in a sense, analogous to ocean areas where sea surface temperatures strongly affect climate and weather, the most famous example being in the Eastern tropical Pacific where El Ninos occur.

The study arguably provides the best estimate ever of the areas where soil moisture changes can affect rainfall, according to the researchers. Extent of water in soil can influence rainfall both regionally and globally. Forecasters, water resource managers and farmers are expected to benefit, once this connection is better understood.

If soil moisture is assumed to affect rain locally, the hot spots tell researchers who study land and atmosphere interactions where to focus their measurements. In general, the hot spots have one thing in common: they occur in transition zones between wet and dry regions.

This was expected, according to the researchers. In wet climates, the sun's energy and cloudiness play a bigger role in determining evaporation rates than soil moisture. In dry climates, the limited water leads to limited evaporation rates, that are simply too small to have a large impact on the atmosphere.

The fact that satellites cannot measure soil moisture through very dense vegetation, is therefore less of a problem. Dense vegetation appears in wet regions, where the hot spots are typically not found.

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