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Historically, the precipitation trend over the past few decades in the Contiguous United States (CONUS) exhibits a "Dry‐West Wet‐East" pattern; this is manifested by recent droughts/floods in the western/eastern US. However, it remains elusive what atmospheric phenomenon has potentially driven such a remarkable, and impactful precipitation pattern. Here we found that a coupled climate mode—the Pacific Meridional Mode (PMM) exerted strong impacts on the precipitation pattern over the CONUS during the summer season. We discovered a significant association between the PMM index and precipitation across the majority of the CONUS; this was manifested as a zonal dipole pattern—negative correlations in the western U.S. along with positive correlations in the eastern and central U.S. Overall, the physical mechanisms based on observations were supported by using Atmospheric Model Intercomparison Project simulations available from the Coupled Model Intercomparison Project Phase 6. Plain Language Summary: Historically, the Contiguous United States (CONUS) was parched in the West and soaked in the East. Despite the importance of this distinct spatial pattern of precipitation variability, the drivers of this hydroclimatic phenomenon remain elusive. Therefore, there is big knowledge gap in understanding the zonal precipitation pattern during the historical period. Here we find that the Pacific Meridional Mode (PMM) can exert strong impacts on the zonal precipitation pattern over the CONUS during the summer season. We discovered a significant association between the PMM index and the precipitation across the majority of the CONUS; this was manifested as a zonal dipole pattern—negative correlations in the western U.S. along with positive correlations in the eastern and central U.S. Overall, the physical mechanisms based on observations were supported by the Atmospheric Model Intercomparison Project experiments of the Coupled Model Intercomparison Project (Phase 6). Our research results explain in large part the zonal precipitation pattern ("Dry‐West Wet‐East") in the CONUS, and perhaps more importantly, the viability of the PMM being used as a potential predictor/indicator for summertime precipitation over the U.S. Key Points: The Pacific Meridional Mode (PMM) exerted strong impacts on the precipitation pattern over the CONUS during the summer seasonThe modulation on precipitation is manifested as a zonal dipole pattern, tied to teleconnections associated PMM sea‐surface temperature anomaliesThe physical mechanisms based on observations were supported by CMIP6 climate model simulations [ABSTRACT FROM AUTHOR]

Calibration of hydrological models for watersheds is critical considering the hydrological processes involved. The Soil and Water Assessment Tool (SWAT) is one such popular model and requires proper calibration, without which models have difficulty in proper simulation of runoff. The present study aims to utilize multi-objective calibration framework using Non-Dominated Genetic Algorithm- II (NSGA-II) and SWAT-Calibration Uncertainty Procedures (SWATCUP) for calibration. The study is conducted on Musi river basin located in India (10,000 Sq km) for seven years from 2013–2016. It includes an initial warm-up period of three years, the calibration period from 2015–2016, and validation period from 2014–2015. NSGA-II aims to optimize the multiple objective functions i.e. Nash Sutcliffe Efficiency (NSE) and Percentage Bias (PBias). The Monthly simulations results are expressed in terms of statistical parameters NSE, R2 and PBias for calibration and validation period. The results indicate satisfactory performance. Further, NSGA-II results are compared with SWATCUP (Sequential Uncertainty Fitting ver.2 (SUFI-2). We find NSGA-II performance is better than SWATCUP. The sensitive analysis indicates that CN2, GW_DELAY, GW_REVAP, ALPHA_BF, RCHRG_DP, and CH_K2 are very sensitive whereas SURLAG, ESCO, SLSUBBS, HRU_SLP are observed to be least sensitive. [ABSTRACT FROM AUTHOR]

During the period 2018–2020, Europe experienced a series of hot and dry weather conditions with significant socioeconomic and environmental consequences. Yet, the extremity of these multi‐year dry conditions is not recognized. Here, we provide a comprehensive spatio‐temporal assessment of the drought hazard over Europe by benchmarking past exceptional events during the period from 1766 to 2020. We identified the 2018–2020 drought event as a new benchmark having an unprecedented intensity that persisted for more than 2 years, exhibiting a mean areal coverage of 35.6% and an average duration of 12.2 months. What makes this event truly exceptional compared with past events is its near‐surface air temperature anomaly reaching +2.8 K, which constitutes a further evidence that the ongoing global warming is exacerbating present drought events. Furthermore, future events based on climate model simulations Coupled Model Intercomparison Project v5 suggest that Europe should be prepared for events of comparable intensity as the 2018–2020 event but with durations longer than any of those experienced in the last 250 years. Our study thus emphasizes the urgent need for adaption and mitigation strategies to cope with such multi‐year drought events across Europe. Plain Language Summary: This manuscript demonstrates that the 2018–2020 multi‐year drought event constitutes a new benchmark in Europe, with an unprecedented level of intensity over the past 250 years. What makes this event truly exceptional compared with past events is its temperature anomaly reaching +2.8 K. This finding provides new evidence that the ongoing global warming exacerbates current drought events. The key message of this study is that the projected future events across the European continent will have a comparable intensity as the 2018–2020 drought but exhibit considerably longer durations than any of those observed during the last 250 years. Our analysis also shows that these exceptional temperature‐enhanced droughts significantly negatively impact commodity crops across Europe. Key Points: The 2018–2020 multi‐year drought shows unprecedented level of intensity during the past 250 yearsThe 2018–2020 event reached record‐breaking +2.8 K temperature anomaly and negatively impacted major cropsFuture drought events reach comparable intensity of 2018–2020 but with considerably longer durations [ABSTRACT FROM AUTHOR]