Search

East Africa frequently faces extreme weather events like droughts and floods, underscoring the need for improved hydrological simulations to enhance prediction and mitigate losses. One of the main challenges in achieving this is low-quality of precipitation data and limitations in modelling skills. Due to drought sensitivity, flood proneness and data availability, the upper and middle stream of the Tana River basin was used as a case to address some of the challenge. We performed convection-permitting (CP) simulations using the Weather Research and Forecasting (WRF) model, and utilizing the CPWRF output as a driver we conducted WRF Hydrological modelling (WRF-Hydro) integrated with the lake/reservoir module. The CPWRF precipitation outperforms the ERA5 using IMERG as the benchmark, particularly for the precipitation amount over mountainous regions and light precipitation events (1–15 mm day-1) in the dry seasons. The improved precipitation especially alleviates the peak false, when comparing the well-calibrated lake-integrated model driven by CRWRF output (LakeCal) to that by ERA5, with an NSE increase of 0.53. Additionally, the lake/reservoir module effectively mitigates the model-data bias, especially for dry-season flow and peak flow, when comparing the lake-integrated model (LakeCal) to the model without the lake (LakeNan), with an NSE increase of 1.67. The lake module makes river discharge more sensitive to spin-up time and affects discharge through lake-related parameters. Adjustments to the lake-integrated model's runoff infiltration rate, Manning's roughness coefficient, and the groundwater component have minimal impact on the dry-season flows. Dividing by the total NSE increase, hydrological modelling improvement is 24 % and 76 % from CPWRF simulation and lake module, respectively. Our findings highlight the enhanced hydrological modelling capability with the lake/reservoir module and CPWRF simulations, offering a valuable tool for flood and drought predictability in data-scarce regions such as East Africa. [ABSTRACT FROM AUTHOR]

The Chinese Loess Plateau (CLP) in northern China is home to one of the most prominent loess records in the world, reflecting past eolian dust activity in East Asia. However, their interpretation is hampered by ambiguity in the origin of loess‐forming dust and an incomplete understanding of the circulation forcing dust accumulation. In this study, we used a novel modeling approach combining a dust emission model FLEXDUST with simulated back trajectories from FLEXPART to trace the dust back to where it was emitted. Over 21 years (1999–2019), we modeled back trajectories for fine (∼2 μm) and super‐coarse (∼20 μm) dust particles at six CLP sites during the peak dust storm season from March to May. FLEXPART source‐receptor relationships are combined with the dust emission inventory from FLEXDUST to create site‐dependent high‐resolution maps of the source contribution of deposited dust. The nearby dust emission areas were found to be the main source of dust to the CLP. Dust deposition across the CLP was found to predominantly occur via wet removal, with also some super‐coarse dust from distant emission regions being wet deposited following high‐level tropospheric transport. The high topography located on the downwind side of the emission area plays an essential role in forcing the emitted super‐coarse dust upward. On an interannual scale, the phase of the Arctic Oscillation in the preceding winter was found to have a strong association with the spring deposition rate on the CLP, while the strength of the East Asian Winter Monsoon was less influential. Plain Language Summary: The dust deposits on the Chinese Loess Plateau (CLP) in northern China provide an extensive record of changes in past dust activity in East Asia. In this work, we combine an atmosphere transport model with a dust emission model to trace the dust backward to where it was emitted. Choosing six locations at the CLP where we traced the dust back to emissions over a 21‐year period during the most active dust months from March until May, for which we investigated how different parts of the CLP were influenced by the different dust emission areas, transport mechanisms, and wind patterns. We find that dust is mainly brought from the emission areas located near the CLP, and that dust from far‐away emission areas in Central Asia has the potential to reach the CLP in smaller amounts. Furthermore, our results show that wet removal of dust by precipitation is important for dust deposition on the CLP, a mechanism that is often overlooked when explaining variations in past dust activity. On a year‐to‐year basis the dust deposition rate over the CLP was found to be connected to the high‐latitude northern hemisphere's climate oscillation (Arctic Oscillation) rather than the regional East Asian winter monsoon. Key Points: The source contribution of emitted dust aerosols to the Chinese Loess Plateau (CLP) is mapped using backward trajectory modelingDistant dust emission regions in Central Asia have a non‐negligible impact on the CLP, with wet deposited dust showing a clearer connectionStrong dust deposition years over the CLP are associated with the negative phase of the Arctic Oscillation [ABSTRACT FROM AUTHOR]

Extreme heat events (EHEs) often hit North China, resulting in significant losses. The devastating EHE in the 1743 summer, marked as the highest temperature in the past 300 years, led to ∼11,000 fatalities. These historical EHEs prompt us to explore potential mechanisms beyond anthropogenic influences. We employ the Norwegian Earth System Model here to simulate the past millennium climate and then dynamically downscale the July 1743 event using the Weather Research and Forecasting Model. The successful simulation of warming in North China, although it has been a fortunate outcome, is supported by tree‐ring records, providing a compelling case study for the event. Through composite and case analyses, we discover a connection between EHEs and active Northeast China Vortexes (NCVs) which induce warm advection, consequently heating the lower atmosphere. Reanalysis further confirms the connection in the modern era. Our study suggests modeling past EHEs, while challenging, is indeed feasible. Plain Language Summary: Nowadays, heat waves have a significant impact on our society and result in substantial economic losses. Climate projections indicate that extreme heat events (EHEs) will become more frequent. However, heat waves have also often occurred in the past 300 years during periods with much lower anthropogenic forcing. One notable example is the severe heat event in the summer of 1743, which killed more than 10 thousand people in North China. The mechanism behind such events remains uncertain, making it exciting and valuable to investigate such heat waves in the past. In this study, we use a global model, a nested regional model, and tree‐ring records to explore the mechanisms driving EHEs. The statistical robustness of the connection between EHEs in North China and Northeast China Vortexes is supported by modern observations. Notably, from 1950 to 2021, 63.6% of EHEs in North China coincide with active Northeast China Vortexes. Key Points: Our simulation, supported by tree‐ring, shows that warm advection linked to Northeast China Vortex likely drove the 1743 extreme heat event (EHE)Reanalysis data from 1950 to 2021 indicate that 63.6% of EHEs in North China coincide with active Northeast China VortexesOur study implies that modeling past extreme climate events is feasible to gain insights into their causes and dynamics [ABSTRACT FROM AUTHOR]

During past glacial‐interglacial cycles, the boreal summer insolation is the most crucial external forcing for climate change. However, the question of whether summer insolation is a key forcing on temperatures in the boreal tropics remains under debate, hampering our understanding of climate change at low latitudes. To shed further light on this issue, we performed a series of equilibrium simulations with the NorESM‐L model over the past 425 ka. Our simulations show that in the boreal tropical monsoon region, the simulated annual temperature is anti‐phased towards the boreal summer insolation. This antiphase relation is also supported by some available geological data. Additional diagnostic analyses reveal that the tropical warmth throughout the year is more reliant on winter temperatures than on summer temperatures. This stands in contrast to the situation in middle to high latitudes, particularly in the Mediterranean region. Further correlation analysis and spectrum analysis suggest that the annual temperature in boreal tropics is highly linked to local winter insolation. Our results highlight complex hydrothermal configurations in the boreal tropics, suggesting a decoupling of temperature and precipitation. Specifically, variations in annual temperature and precipitation in the boreal tropics are driven by distinct patterns of seasonal insolation. We deduce that the unique hydrothermal configurations in North Africa may have influenced the dispersal of early humans out of Africa. Plain Language Summary: On the orbital timescale, whether the temperature in boreal tropics is driven by boreal summer insolation still remains unclear. In this study, we conduct a comprehensive analysis of simulated results spanning the 425 ka. Our findings indicate that the annual temperature in boreal tropics is anti‐phased to the local summer insolation. Specifically, when local summer insolation is high (low), overall cooling (warming) occurs in the North African and South Asian monsoon regions. Some available paleo‐temperature records from the tropics also provide partial support for our simulation results. The temperature pattern in the boreal tropics is linked to the strong internal feedback in the summer from the unique climate background of the tropics, which results in relatively slight summer cooling at high boreal summer insolation, while the annual temperature is largely dependent on winter temperatures driven by local winter insolation. Our simulations reveal highly complex hydrothermal configurations in the boreal tropics on the orbital timescale, suggesting a decoupling of temperature and precipitation, with the former influenced by winter insolation and the latter forced by summer insolation. Key Points: The temperature in boreal tropical monsoon regions is anti‐phased to the boreal summer insolationThe annual temperature in boreal tropics is more dependent on the winter than summer temperaturesThe key role of local winter insolation in regulating the boreal tropical temperature is closely linked to its unique climatic background [ABSTRACT FROM AUTHOR]

During the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO 2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO 2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles. [ABSTRACT FROM AUTHOR]

Off the Northwestern Iberian Peninsula, the vigorous bottom-current regime interacts with a complex seafloor topography inside the Galicia Interior Basin (GIB), which was tectonically shaped during the opening of the North Atlantic Ocean basin in Cretaceous times. The evolving North Atlantic Ocean circulation determined the depositional pattern of the basin fill over time, which can, in turn, be utilized as palaeoceanographic archive. This study reconstructs the evolution of the GIB sedimentary system since the mid-Eocene, namely, resulting from interplay between down- and along-slope sediment-transport processes, using high-resolution multichannel seismic data. Six major depositional stages are identified and connected to the evolution of the North Atlantic Ocean circulation. 1) Levelling of topography shows that the influence of contourparallel bottom currents on the depositional pattern steadily intensified since the mid-Eocene; 2) The strengthening of Northern Component Water (NCW), associated with the opening of the Faeroe- Shetland Basin in the late Eocene, is documented along the southwestern European continental margin for the first time by the onset of a plastered contourite drift; 3) A shift in the depocenters provide evidence that the closure of the Tethys-Indian Seaway led to Tethys Outflow Water into the Atlantic Ocean at intermediate ocean depths in the Miocene; 4) Until the mid-Miocene, the tectonic stress regime initially associated with the Pyrenean Orogeny and the following Betic Orogeny led to both sets of small-scale faulting systems as well as submarine mass wasting indicated by slope scarps and mass-transport deposits; 5) The onset of modern-style Mediterranean Outflow Water (MOW) after the Messinian Salinity Crisis (5.3 Ma) caused a distinct change in the depositional dynamics from combined along- and down-slope transport processes towards predominantly contouritic deposition, which is evident from the construction of several separated mounded contouritic drifts that formed during Pliocene and early Pleistocene times; and 6) The contourite drift growth continued during the middle and late Pleistocene, but under a gaining influence of down-slope processes. [ABSTRACT FROM AUTHOR]