Monitoring of agricultural drought from remote sensing products and in-situ meteorological data

The extreme events increasingly present in the Pacific (El Nino / La Nina phenomena) have significant consequences on island territories. The effect of climate change and drought episodes is therefore a central concern in many Pacific islands like Vanuatu, Wallis-and-Futuna, French Polynesia, etc. The intense drought events have undeniable impacts on biodiversity, agricultural crops and water resource, as was the case in 2019 for New Caledonia. In particular, projections in New Caledonia count on a possible increase in temperatures of 3°C and a water deficit of 20% in 2100 with longer and more intense drought episodes and an even greater west coast/east coast disparity (Dutheil, 2018). To date, the monitoring and anticipation of these drought episodes is done via meteorological measurements providing information on the rainfall deficit and not on the water stress of plants. In addition, the data are only available on a few measurement points and are not continuous over the territories.

In order to meet this need, a tool for monitoring environmental and agricultural drought using satellite images and meteorological data is being developed and validated in New Caledonia: Earth Observations for Drought Monitoring (EO4DM) project. This project is carried out in collaboration with Météo-France NC as a technical partner and the local Rural Agency as end user, and aims to provide a tool to help decision-making to institutions and management assistance for farmers. This solution will provide data constituting a singularly important source of information whose valuations and contributions can be multiple: agriculture, resource management (water), security (monitoring of risks linked to floods, fires), environment, etc.

To do so, various surface indices reflecting the state of the vegetation and certain soil properties such as humidity and temperature were estimated from different satellite sensors (MODIS, Sentinel-2, Landsat-8, ASCAT) in order to address different space scales from the field to regional scale. These indices were normalized over a relatively long period, allowing access to drought indicators: VHI (Vegetation Health Index; Kogan et al., 1997), VAI (Vegetation Anomaly Index; Amri et al., 2011), MAI (Moisture Anomaly Index; Amri et al., 2012) or TAI (Temperature Anomaly Index; Le Page and Zribi, 2019). Combined with in-situ meteorological products like SPI (Standardized Precipitation Index; McKee et al., 1993) and SPEI (Standardized Precipitation Evapotranspiration Index; Vicente-Serrano et al., 2010), these indicators assess the intensity of drought episodes and estimate their severity over the entire territory.