Drought monitoring and adaptation strategies in agriculture

Droughts are becoming more widespread, frequent and severe aggravated by climate change, necessitating the alignment of drought monitoring and adaptation strategies. Effective and timely drought monitoring is essential for successful implementation of drought adaptation strategies, which enhance the ability to anticipate, respond to, and recover from drought events. Drought monitoring and adaptation strategies together are pillars of a risk-based drought management approach, which is proactive and more sustainable than a crisis-driven responsive approach. Agriculture is the most vulnerable sector to drought impacts spanning from reduced crop yield to complete crop failure. Since agronomic drought adaptation strategies are implemented at a plot scale, it also becomes relevant to integrate drought monitoring at the farm scale. Accordingly, this study aims to demonstrate plot scale drought monitoring and to evaluate different local drought adaptation strategies. The first study of this dissertation explored the integration of short-term plot-based soil moisture measurement for agricultural drought monitoring. Cosmic ray neutron sensor (CRNS), a non-invasive and innovative tool, was used to obtain representative soil moisture measurements at plot scale, from two agricultural sites in Germany. A Soil Water Deficit Index (SWDI) was computed based on the CRNS daily soil moisture measurements and inherent soil physical hydraulic characteristics. Subsequently, by adopting the conceptual framework implemented by the European Drought Observatory (EDO), the SWDI values were integrated into the combined drought indicator replacing the model-simulated soil moisture anomaly indicator. Results revealed the CRNS soil moisture measurement indicated the drought propagation in agreement with the corresponding anomaly-based standardized precipitation index (SPI) values. However, the vegetation drought indicator, anomaly Fraction of Absorbed Photosynthetically Active Radiation (zFAPAR) used by EDO either underestimated the drought generally or did not clearly show the response to irrigation application. Consequently, zFAPAR was replaced by a vegetation condition index (VCI), which detected drought in agreement with SWDI and showed the response of the crop following the irrigation application. In the second study, the effect of conventional tillage practices (moldboard, chisel plow and disk harrow) on soil moisture content during a drought period was evaluated, based on field measurements using CRNS and point sensors. Further, the conservation tillage practices (no tillage and mulching), proposed as drought adaptation strategies, were simulated using the Decision Support System for Agrotechnology Transfer (DSSAT) model. The analysis results revealed temporal variability in soil moisture dynamics during the observation period between different tillage methods. Markedly, soil moisture measurements below the working depths of the conventional tillage methods were the lowest under the moldboard tillage method, attributed to the compacted pan layer impeding water movement. The DSSAT simulation showed better agreement with the CRNS measurements than with point measurements. Soil water balance simulation with DSSAT model also indicated reduced soil evaporation by 40 \% on average when crop mulch was used in tandem with conventional tillage. The third study assessed deficit irrigation and soil amendment as drought adaptation strategies to achieve optimum crop yield per less water consumption. Recognizing evapotranspiration as proportional to crop water consumption, the response of wheat to water stress by adjusting its evapotranspiration requirements under combinations of drought adaptation treatments was assessed. It was noticed that using soil amendment materials improved the water retention of sandy soil in the current experiment, which yielded an optimum water use efficiency when combined with deficit irrigation administered beginning from the mid growth stage of wheat. Overall, this study evaluated soil moisture as an integral parameter in agricultural drought monitoring. However, since drought is a gradual process, its entire development might not be captured by a single drought index. Therefore, soil moisture is integrated with precipitation and crop-based indicators for detecting drought initiation, consolidation, and recovery from it. In addition, the combination of various adaptation strategies proves to be more beneficial in alleviating the impact of drought than single approaches. Yet, the implementation of drought adaptation applicable to every situation requires a preliminary assessment that considers factors such as soil and crop type. A drought management approach that entails the implementation of drought adaptation strategies informed by timely drought monitoring is crucial for mitigating the impact of droughts on agricultural productivity.