Monitoring of agricultural drought using Crop Moisture Stress index and the estimation of resulting maize yield reduction

Abstract

<p>The drought in south-eastern Europe in the summer of 2017 heavily affected agricultural production, subsequently decreasing yields of maize. The European Drought Observatory provides Combined Drought Indicator for a 10-day period with coarse spatial resolution of 5 km, which is not localized on field level. It is derived from the combination of Standardized Precipitation Index (SPI), the Soil Moisture Index Anomaly (SMA), and the anomaly of the fraction of absorbed photosynthetically active radiation (FAPAR). Monitoring moisture levels in crops can provide timely information about the presence of abiotic stress in plants and improper development within a growing season. Heat stress and low levels of moisture in maize during summer can thereafter have detrimental consequences on yield. For that reason, in this study, the crop moisture level was estimated at specific parcels by calculating the normalized difference moisture index (NDMI) from Sentinel-2 multispectral imagery during summer months (June–July–August) and the time-series of NDMI were analyzed. Based on the average NDMI value in July, the crop moisture stress (CMS) index was calculated and divided into six classes. Maize yield data on parcel level were provided by an agricultural company for the period 2017 – 2021 in the Backa region of Vojvodina province, Serbia. Yield data for the period 2017-2020 were used to calculate average yield for each class of CMS, whereas yield data from 2021 were used for validation. Mean absolute error (MAE) and root-mean-square error (RMSE) were calculated and were around 1 t/ha. The results showed that the CMS values at a specific parcel could be used for within-season estimation of maize yield and the assessment of drought effects. Also, the CMS index was tested for the 2022 growing season which had drought hazard conditions in south-eastern Europe according to the European Drought Observatory. Expected maize yield reduction estimated for specific scouted fields showed substantial and below average yield values.</p>