The objective of this book is to raise awareness in the hydrologic community of the important changes that have occurred in the climate and hydrology of the La Plata basin during recent decades. In a context of global climate change and of great regional changes, the assumption that series of climatological and hydrological observations are stationary must be regarded with suspicion. This book therefore presents an overview of the few available techniques for assessing future climate and hydrology.

The IWMI World Water and Climate Atlas gives irrigation and agricultural planners rapid access to accurate data on climate and moisture availability for agriculture. The Atlas includes monthly and annual summaries for precipitation, temperature, humidity, hours of sunshine, evaporation estimates, wind speed, total number of days with and without rainfall, days without frost and Penman-Montieth reference evapotranspiration rates.

This paper describes how farmers in the South-Western Highland of Tanzania predict rainfall using local environmental indicators and astronomical factors. The perceptions of the local communities on conventional weather and climate forecasts were also assessed. Systematic documentation and subsequent integration of indigenous knowledge into a conventional weather forecasting system was recommended as a strategy that could help to improve the accuracy of seasonal rainfall forecasts under a changing change.