Multi-scale topography assessment for site-specific drought management in Sweden

Abstract: Globally, as well as in Sweden, the occurrence of droughts is expected to increase due to global warming. The drought summer of 2018 revealed the vulnerability of Sweden’s agriculture – with cereal yield losses of up to 50 %. Subsequently, the development of more resilience crop production systems to mitigate future droughts is required. Precision agriculture practices (PAP), widely applied in Sweden, are promising to base such developments upon. Hence, the aim of this study was to investigate the potential usage of topography for site-specific decision support, to extend PAP for advanced drought management in Sweden. Therefore, the drought effect along the study period (between crop development stages DC31-DC75) on crop growth development and related to field topography was assessed in a dry year (2018) and compared to a non-dry year (2019). Two common cereals i.e., Winter wheat and spring barely were selected to conduct this study. The study area was in the south-eastern region of Skåne in Sweden. The scale varied from the whole study area to within the field. Crop growth development was monitored using different vegetation and drought indices i.e., normalized difference vegetation index (NDVI), normalized difference red-edge index (NDRE), normalized difference water index (NDWI) and the normalized difference drought index (NDDI). Topography was analysed at and within the field using different topographic indices i.e., slope, relative height (RE) and the topographic wetness index (TWI). The data required to conduct this study was publicly available and consisted of a highresolution digital elevation model, Sentinel-2 remote sensing data, weather data, field polygon as well as soil texture data. Overall, the results clearly showed an average NDVI, NDRE and NDWI reduction over the study period in 2018 compared to 2019 for both cereals; this reduction was about 25 %, 32 % and 58 % for winter wheat and about 36 %, 43 % and 69 % for spring barley. Topographic related within-field crop growth variations were prominent under dry conditions in 2018 and not present under non-dry conditions in 2019. Within-field crop growth variation increased with an increase in average field slope under dry conditions. The TWI was the most promising index explaining within-field crop growth development. Further studies should include other sitespecific field characteristics besides topography to better delineate within-field drought management zones for PAP.