Towards a Hazard Warning System for Droughts and Floods Associated with Climate Variability in Southwest Asia

Climate variability-associated droughts and floods are recurrent phenomena in Southwest Asia. For example, in Iran the statistical probability of the recent (1999-2001) persistent multi-seasonal drought is once every 30 years. The rainfall data of the last 32 years indicate that, in 16 years, precipitation was lower than the long-term mean. Out of 16 years, seven received 30 percent less precipitation than the long-term average. 

A review of recent research to understand climate variability and manage recurrent natural hazards reveals:

• A significant correlation exists between SOI and autumn rainfall (October-December) in the southern foothills of the Alborz Mountains, northwestern districts and the western margin of the Caspian Sea in Iran. El Niño is associated with higher than normal rainfall and La Niña with lower than normal rainfall in these areas during autumn.
• However, in large areas of Iran, El Niño is associated with droughts during winter (January-March).
• No relationship between SOI and surface air pressure and wind direction has been established. 
• It is probable that ENSO could influence the climate through upper air pressure systems over Iran.
• A preliminary study by IRI indicates a possible mechanism through which La Niña could cause droughts in Southwest Asia.

Given numerous existing constraints to utilizing such research findings for generation and use of climate forecast information at local level for modifying decisions, there is a need to rely on precursor indicators pertaining to microclimatic peculiarities of Southwest Asia. A hazard warning system based on the following factors could be considered:

• The bulk of food (cereal) production depends on the region’s irrigation water that, in turn, relies on the melting snows that feed river networks. Snow also provides necessary soil moisture in rain-fed areas.
• It is the accumulated winter snow from the high mountains that sustains agriculture, and the changing conditions down the length of the snow-fed river valleys that create varying production possibilities. 
• The depth of snow pack (December-March) and temperature variation (March-May) determine the potential availability of water for ensuing months, and the availability of stored soil moisture for spring, summer and subsequent winter crops. 
• Snow deposition by enhancing soil moisture contributes to pasture growth on grazing lands and availability of fodder on irrigated lands. 
• Timing of accelerated snow melting due to higher temperature could be beneficial as well as hazardous. For example, a mid-May 1999 accelerated snowmelt was untimely both for ripening the wheat crop and the yet-to-be planted second cereal crop in northeastern provinces in Afghanistan. On the contrary, a similar accelerated snow melting at the end of April 2001 benefited the wheat crop that was at the grain filling stage, resulting in higher yields.

It is possible to evolve a hazard warning index keeping in view the depth of snow pack and temperature variables based on past historical analogues relevant to specific microclimatic locations. This effort could draw usable information from the ongoing research on SSTs and climate variability in Southwest Asia. A framework for the identification of decision points in the agricultural planning cycle, and use of climate information for crop planning and livestock management, has been evolved based on snow deposition and temperature variation parameters. This framework requires validation at ground-level for fine-tuning and application. 

A R Subbiah is presently working as a Program Manager, Extreme Climate Events and Climate Forecasting Applications in Bangladesh. He can be contacted at subbiah@ait.ac.th