Monitoring crop growth conditions using the global water satisfaction index and remote sensing

Water availability is one of the limiting factors to crop growth in arid and semi-arid zones. Shortages of fresh water become very serious for different regions of the world with important consequences for food security. Early warning systems based on the integrative use of remote sensing observations and crop growth modelling have been developed and implemented for specific regions. The Joint Research Centre, Ispra (Italy) initiated the MARS project (Monitoring Agriculture with Remote Sensing). Nowadays, this system is used operationally to forecast crop yield across Europe. To produce global real-time water balance calculations and outputs a system has been developed called GWSIx (Global Water Satisfaction Index). The GWSI model is based on a simple soil water balance model, which is used to assess the impact of weather conditions on crop growth. The water balance used is known as the FAO Crop Specific Water Balance, CSWB. The system developed delivers actual information on crop growth conditions for the major food crops per country per decade (periods of 10 days) and per 0.1 by 0.1 degree grid cell. It was found that the developed method delivers indications for the occurrence of crop stress. The spatial distribution of available water and crop development at different scales can also be described by applying remote sensing observations. Quantitative information dealing with space-time distribution of water can be obtained through the mapping of crop surface evapotranspiration. However, application of such an approach at global scale is hardly possible. NDVI time series as derived from NOAA AVHRR satellite observations have been used extensively to monitor vegetation development at different scales. To assess agricultural crop growth conditions we used the Global Inventory Modelling and Mapping Studies (GIMMS) dataset of the NASA. It contains bimonthly NDVI data in an 8-km global raster as derived from NOAAA AVHRR satellite observations for the period 1982-2002. Output of the GWSI system has been compared with results obtained through remote sensing. Preliminary results are presented