Karumuri Ashok

The Indian Ocean dipole (IOD) mode events are one of the most fascinating interannual ocean-atmosphere phenomenon in the tropical Indian Ocean. The zonal contrast of tropical ocean conditions foists enormous unfavorable impacts on the regional weather and climate. Until recently, the predictability of IOD events was limited to only a season in advance which poses a huge socioeconomic loss in the affected regions. We explore the DCPP-CMIP6 decadal hindcast models for their predictability of IOD events at different years after their initialization. Two CMIP6 models viz., CanESM5 and NorCPM1 (to some extent) have quite significant prediction skills for IOD events even after eight to ten years of initialization. We study these two models to probe the features that impact the IOD predictability. Customized version of model components, refined ocean-atmosphere coupler and sophisticated data assimilation system are the major attributes to their skill for IOD predictability. It is evident from CanESM5 simulations that Southern Ocean provides notable signals through Antarctic circumpolar currents that propagate to tropical Indian Ocean and influence the IOD events.

This study comprehensively assesses the seasonal prediction skill of precipitation over the Middle East (ME), with a particular focus on the Arabian Peninsula (AP), using the APEC Climate Center (APCC) multi‐model ensemble (MME) system. Analysis of one‐month lead hindcasts (1993–2016) shows that the MME consistently outperforms individual models and shows higher skill during boreal spring and autumn. These seasons exhibit strong teleconnections with tropical SST‐based climate drivers, such as El Niño‐Southern Oscillation (ENSO), El Niño Modoki, and the Indian Ocean Dipole (IOD), while forecast skill remains lower in boreal summer and winter. Teleconnection analyses reveal that the MME's skill is closely linked to its ability to capture SST‐driven precipitation variability. Forecast skill significantly declines when regression‐based precipitation signals from climate drivers are removed, highlighting the importance of these teleconnections. Although the MME exhibits overall superior performance, challenges remain in simulating winter precipitation over the AP, where the influence of climate drivers is relatively weak and models struggle to accurately reproduce teleconnection patterns. These findings underscore the value of improving the model representation of teleconnections to enhance seasonal forecast reliability. The results provide actionable insights for enhancing dynamical prediction systems and inform future model development tailored to this climate‐sensitive region.

The desert climate of the Arabian Peninsula (AP), marked by sparse rainfall, extreme temperatures, and frequent dust events, significantly impacts its 80‐million population, environment, and economy. Rising temperatures and dust incursions exacerbate these harsh conditions, yet the AP's climate is underrepresented in global climate research. Understanding its variability is crucial for improving predictions on subseasonal‐to‐seasonal timescales and for developing reliable climate change projections. Existing climate models fail to capture the region's unique environment, topography, and land‐use changes, leading to poor representation of key processes like local convection, aridity, and moisture transport. To address these gaps, Saudi Arabia established the Climate Change Center (CCC) in 2022, part of the Saudi Vision 2030 initiative. The CCC aims to study climate variability and project future changes using advanced Earth system models developed in collaboration with international partners. This study presents the CCC's roadmap, focusing on its relevance for global climate research and policymaking, including the Saudi and Middle East Green Initiatives. We also discuss regional uncertainties in the IPCC's climate projections for the AP and highlight the development of high‐resolution regional models that account for local atmospheric, land, and oceanic processes. The CCC is developing subseasonal‐to‐seasonal forecasting systems and drought monitoring tools, alongside user‐friendly dashboards to offer stakeholders customized climate data. These tools, set for launch in 2025, will aid informed decision‐making in addressing extreme weather events and climate‐related challenges in Saudi Arabia.

Understanding extreme precipitation events (EPEs) in the Arabian Peninsula is crucial for managing climate risks. This study evaluates EPEs using data from rain-gauge, high-resolution reanalysis, and CMIP6 and NEX-GDDP model simulations. A multi-criteria evaluation framework identifies top-performing models and addresses biases in precipitation products. Results reveal a peak-point structure in the precipitation-temperature relationship, with precipitation intensity following Clausius-Clapeyron (CC) scaling up to the peak-point temperature, beyond which it decreases. Future projections under SSP5-8.5 indicate a significant 5°C shift in peak-point temperature by the end-of-the-21st-century. CMIP6 models exhibit super-CC scaling (~11%/°C), while NEX-GDDP shows a lower rate (~4-5%). EPE precipitation accumulations increase by 10 to 35% per °C warming, with intense events becoming more frequent (up to 20%). Southern and coastal AP show intensified EPEs, while northern AP shifts to EPE-dominated regimes despite declining total precipitation. These insights advance understanding of regional hydrological dynamics and inform climate adaptation strategies.

The Eastern Tropical Pacific (ETP), Arabian Sea (AS), and Bay of Bengal (BoB) are recognized for hosting the most intense oxygen minimum zones (OMZs), characterized by severe hypoxia at intermediate depths (Gilly et al., 2013; McCreary et al., 2013). The formation of these OMZs is attributed to a complex interplay of physical and biogeochemical processes, many of which exhibit commonalities across all three basins. Enhanced primary productivity in surface waters fosters organic matter export to deeper layers. This organic matter undergoes intensified decomposition at intermediate depths, leading to oxygen depletion through microbial respiration (Breitburg et al., 2018; Gilly et al., 2013; Paulmier and Ruiz-Pino, 2009; Pennington et al., 2006). Furthermore, sluggish circulation patterns within these basins limit the advection of oxygen-rich waters into the OMZ, and weak vertical mixing restricts oxygen replenishment from the surface (Breitburg et al., 2018; Gilly et al., 2013; Paulmier and Ruiz-Pino, 2009; McCreary et al., 2013).The Bay of Bengal oxygen minimum zone (BoB-OMZ) deviates from the typical pattern observed in the ETP and AS despite sharing common drivers for OMZ formation (Gilly et al., 2013; McCreary et al., 2013). This disparity underscores the significant influence of regional factors on the BoB-OMZ’s characteristics. A key distinction lies in the primary mechanism responsible for its persistence. Microbial processes such as denitrification and anammox are crucial for oxygen consumption in the ETP and AS (Rao et al., 1994; Gilly et al., 2013; Kalvelage et al., 2013; Castro-González et al., 2014). In contrast, the BoB-OMZ primarily owes its existence to intense salinity stratification (Paulmier and Ruiz-Pino, 2009; Sarma et al., 2018; Udaya Bhaskar et al., 2021). This stratification effectively traps oxygen-depleted waters, hindering vertical mixing and oxygen replenishment from the surface. Cyclonic eddies further influence the intensity and distribution of the BoB-OMZ (Sarma et al., 2018). Interestingly, anticyclonic eddies can sporadically ventilate the BoB-OMZ with oxygen-rich surface waters, leading to temporary weakening and spatial heterogeneity of the hypoxic zone (Sarma and Udaya Bhaskar, 2018). These contrasting mechanisms, absent in the ETP and AS, contribute to the BoB-OMZ’s weaker overall intensity and dynamic nature.The intensity and extent of the BoB-OMZ exhibit significant spatial and temporal variations. In the northern BoB, influenced by major river discharge from the Ganges and Brahmaputra rivers, the summer monsoon and post-monsoon seasons see intensified salinity stratification, leading to a more pronounced OMZ (Howden and Murtugudde, 2001; Jana et al., 2015; Udaya Bhaskar et al., 2021; Sarma et al., 2016). This stratification traps oxygen-depleted waters, hindering vertical mixing and oxygen replenishment. Additionally, the cross-shelf transport of organic matter from the western BoB fuels microbial decomposition, resulting in a stronger OMZ compared to the eastern region (Udaya Bhaskar et al., 2021). Recent studies suggest the possibility of even more intense OMZ formation in the northwestern BoB during winter (Bristow et al., 2017), potentially due to enhanced nutrient input from rivers or atmospheric deposition. However, Sridevi and Sarma (2021) propose that these intense episodes might be transient features caused by eddies. Biogeochemically, the BoB-OMZ is considered weaker compared to other regions. This can be attributed to factors such as weak upwelling, limited primary productivity, and rapid sinking of organic carbon to the deep sea, reducing the availability of organic matter for microbial oxygen consumption (Rao et al., 1994; Ittekkot et al., 1991; Naqvi et al., 1996; Ramaiah et al., 2010; McCreary et al., 2013). Furthermore, several studies suggest that riverine nutrients are rapidly consumed within a limited distance (20 km) from the coast, restricting their contribution to offshore OMZ intensification (Howden and Murtugudde, 2001; Sarma et al., 2018).The Godavari River, India’s third-longest fluvial system (1,465 km), is driven by the monsoon cycle, resulting in concentrated discharge from July to September (Central Water Commission, 2019). This peak discharge coincides with the BoB’s highest riverine input, contrasting with the dominance of tidal processes in other seasons (Howden and Murtugudde, 2001; Sarma et al., 2010). While the influence of major rivers such as the Ganges and Brahmaputra on the northern BoB-OMZ is well-established (Jana et al., 2015; Udaya Bhaskar et al., 2021), the annual impact of medium-sized rivers such as the Godavari remains less explored. This study addresses this knowledge gap by investigating the annual cycle of Godavari River discharge (GRD), its potential effects on local coastal primary productivity, and its contribution to the development of a seasonal OMZ near the river mouth. The following section outlines the methodology and details the datasets employed. Section 3 presents our findings on the seasonal evolution of the BoB- OMZ, the biogeochemistry in the river mouth region, and the potential mechanisms driving the intense OMZs observed near the Godavari. Finally, section 4 provides a comprehensive summary and concluding remarks. The GRD data utilized in this study were obtained from the Dowleiswaram barrage, located approximately 50 km upstream of the river’s confluence with the BoB. This barrage serves as the final major infrastructure point along the Godavari’s course, regulating the downstream flow of freshwater into the BoB. Daily measurements of water released from the Dowleiswaram barrage provided a high- resolution record of GRD variations. These daily values were subsequently aggregated to generate monthly mean time series data...

Introduction: This study investigates the biogeochemical impact of Godavari River discharge (GRD) on the Bay of Bengal (BoB), focusing on the formation of an intense and shallow oxygen minimum zone (OMZ) near the river mouth during the fall season. Unlike the BoB’s typical intermediate-depth OMZ, this subsurface (~40-200 m) phenomenon is attributed to the interplay of GRD-driven nutrient enrichment, coastal upwelling, enhanced productivity, and subsequent organic matter decomposition.Data and Methods: Our analysis using the Biogeochemical-Argo floats and World Ocean Atlas 2018 data reveals that a clear shoaling and intensification of the OMZ in the fall season. Further, a comparative analysis at two geographically distinct locations highlighted the pivotal role of GRD.Results, Discussion, and Implications: The location directly influenced by GRD exhibited significantly higher chlorophyll-a blooms, net primary production during the southwest monsoon, and pronounced oxygen consumption during the fall compared to the other. Our analysis suggests that GRD fuels primary productivity, leading to organic matter abundance and intense oxygen depletion in the subsurface layers, driving the observed shallow OMZ. Understanding the complex interplay between GRD, stratification, upwelling, and biogeochemical processes is crucial for predicting the impact of altered riverine inputs on coastal ecosystems, greenhouse gas emissions, and the overall health of the coastal BoB.

Land surface processes such as the soil moisture—air temperature coupling influence compound climate anomalies like heatwaves and droughts, yet the spatial and temporal variability of the coupling strength is still understudied. We assess global land exposure to concurrent heat waves and drought since the 1980s. We found that drought significantly shapes the spatial distribution of the risk of heat waves. We show that the portion of global land experiencing drought‐conditioned heat anomalies more than tripled in less than 3 decades. However, using such traditional heat waves indicators, the level of spatial coupling between heat waves and drought seems to decline. Conversely, time‐dependent approaches accounting for the baseline climate change offer a more stable perspective. We conclude that tailoring hazard definitions to specific processes and impacts is crucial. Early warning systems can play a prominent role in mitigating the impacts of global warming to society.