Monsoon Precipitation Research Articles

Unraveling the climate control on debris-free glacier evolution in the Everest region (Nepal, central Himalaya) during the Holocene

Current mass balance and meteorological surveys of Mera glacier located about 30 km south of Mount Everest in Nepal show the dominant role of Asian monsoon precipitation on interannual mass balance variability while temperature controls the altitude of snow-rain threshold. As these observations on mass balance variability only explore the recent decades, studies on paleo glacial extents are useful to investigate the long-term climate forcing on glacier evolution. To do so, we investigated the long-term evolution of the debris-free Mera glacier and a neighbouring small debris-free South Khare glacier. Fifty-one 10Be CRE ages were obtained from samples collected on moraine boulders and roches moutonnées. 10Be CRE ages of the boulders span from the end of the Lateglacial (19.0–11.7 ka) to the Little Ice Age (∼0.6–0.1 ka). The oldest dated moraine in this study was observed at the base of South Khare glacier with an age of 13.6 ± 0.5 ka. The two glaciers subsequently experienced their largest Holocene extent in the Early Holocene with moraines dated to 11.0 ± 0.3 ka at the base of Mera glacier and 10.8 ± 0.5 ka at the base of South Khare glacier. We did not observe any moraine from the Mid-Holocene. During the Late Holocene several glacier advances were recorded around 2.3 ± 0.2 ka, 1.5 ka and then during the last centuries at Mera glacier and around 2.8 ± 0.6 ka, and during the Little Ice Age at South Khare glacier. To explore the links between long-term Nepalese glacier changes and climate, we used oceanic and terrestrial Indian Summer monsoon reconstructions and temperature and precipitation output from two transient global climate models TraCE and LOVECLIM. These climate data outputs were corrected by a reconstruction of the Atlantic Meridional Overturning Circulation (AMOC) over the Holocene and its associated climatic impacts. We also used sensitivity experiments from the IPSL (Institut Pierre Simon Laplace) model to discuss the possible influence of horizontal resolution, land hydrology, vegetation and runoff on changes in Asian summer monsoon. Importantly, we show this long-term Nepalese glacier pattern does not perfectly conform neither to the Indian monsoon precipitation that is documented from terrestrial and marine records nor to temperature and precipitation changes simulated by the models. While the maximum glacier extent in the Early Holocene corresponds to enhanced precipitation documented by proxies and models, the Late Holocene glacier advance remains puzzling. We claim that new paleo glacier records and improved climate simulations are necessary to get a better understanding of past glacier changes and the associated climate dynamics, which might be crucial to gain confidence in both glacier and climate future evolutions.

Recent and projected changes in water scarcity and unprecedented drought events over Southern Pakistan

In recent decades, water scarcity is a significant constraint for socioeconomic development and threatens livelihood in an agriculture-based developing country like Pakistan. The water crisis in the country is projected to exacerbate in the coming years, especially in the southern parts. This dire situation calls for an investigation of major droughts, associated water scarcity, and changes in teleconnection patterns over Southern Pakistan. Moderate to low Southeastern monsoon (SEM) precipitation triggered the extreme drought episode (2017–2020) over Southern Pakistan and intensified the water scarcity. This study explored the severity of the respective drought event, underlying mechanisms, and changes in water scarcity over Southern Pakistan. To investigate the future changes (1980–2050) in water scarcity, coupling models (global hydrological models (GHMs)-global climate models (GCMs)) have been used to achieve the interannual performance of water availability and total water consumption. Besides, future scenarios used in this study are the combinations of SSPs and RCPs, including middle-of-the-road (SSP1-RCP4.5) and fossil-fueled development (SSP2-RCP8.5). The findings indicated a precipitation deficit of 45% during the 4-year (2017–2020), depicting the worst events in the past 50 years. South Pakistan observed the worst SEM droughts over the last 50 years, as 2000–2005 was the worst drought (precipitation deficit of 75%), followed by 2017–2020 with a 49% of precipitation deficit. Water scarcity was exacerbated by the extreme dry spells that developed over most of southern Pakistan between 2017 and 2020 as a result of moderate-to-exceptionally low SEM precipitation. Furthermore, this drought episode was accompanied by the cool phase in the Pacific and equatorial Indian Oceans. The future changes in water scarcity over the southern regions of Pakistan present a sharp increase under the SSP2-RCP8.5 scenario and are anticipated to be intensified in already stressed regions. This research is essential for environmentalists, and water resources managers, and provided crucial information to identify the hot spot areas in the target region so that water scarcity problems could be reduced in the future.

Late Quaternary evolution of Daihai Lake in northern China and implications to the variation of the East Asian summer monsoon

Global warming over the past decades has resulted in desiccation of lakes in arid and semi-arid northern China. However, the mechanisms responsible for the sharp fluctuations in water levels for these lakes in this region are still unclear. The water level fluctuations in geological time can provide an analogue to better understand current lake levels’ response to global warming. In this study, a combination of quartz and feldspar luminescence dating techniques was applied to establish the chronologies of two sedimentary sequences related to lake level in the catchment of Daihai Lake, located on the fringe of the East Asian summer monsoon (EASM) domain. Our objective is to reconstruct the late Quaternary history of lake level fluctuations and provide the interpretations of their causes. The results indicate that two lake-level highstands existed during 130–120 ka and 8-4 ka, at least ∼38 m and 40 m above the current lake level, respectively. We interpret that the lake level variations on multiple timescales in the monsoonal marginal area have primarily been regulated by the EASM intensity and corresponding monsoonal precipitation, while temperature changes may have played a minor role. Moreover, a compilation of existing lake level data reveals that EASM intensity has a complex response to changes in Northern Hemisphere summer insolation on millennial-orbital timescales. Combining precipitation records in central and southern China, the character of rainfall across East Asia during MIS 5 exhibits a dominant tripolar pattern.

Megacycles of climate and vegetation in East Asia since 3 Ma

Although there are numerous long-term terrestrial climate records based on biological and other indicators spanning the last 3 Myr in Asia, there are few studies on the vegetation evolution on a continental scale. Here we present a long (∼3 Myr) pollen record from core LN-1 from the North China Plain. The record shows that during the interval of 3.0–1.2 Ma, prior to the Mid-Pleistocene transition, the vegetation of the North China Plain was mainly open deciduous broadleaved forest, and that there were five cool and dry phases when conifers and herbs expanded: during 2.7–2.6 Ma, 2.2–2.1 Ma, 1.75–1.85 Ma, 1.5–1.6 Ma, and 1.3–1.4 Ma. Comparison with other pollen records from the East Asian monsoon region reveals a similar series of cool and dry intervals. These extended cool and dry intervals occurred during a period of high Earth orbital eccentricity, and were most likely related to the status of the global ocean carbon reservoir, under eccentricity forcing. We suggest that feedback from the terrestrial vegetation may have interrupted the dominant 41-kyr climatic cyclicity associated with middle and high latitudes of the Northern Hemisphere that had persisted since the Late Pliocene. After 1.2 Ma, the vegetation of the North China Plain changed to steppe and shrub steppe, while at the same time grassland expansion and forest recession occurred in northern China. The associated global cooling led to decreases in ocean temperatures, land-sea exchanges, and monsoon precipitation, which together drove the aridification of the Asian interior. We combined our data with eight published pollen records, and the zonal vegetation maps for East Asia since 3 Ma were generated.

Quantification of tropical monsoon precipitation changes in terms of interhemispheric differences in stratospheric sulfate aerosol optical depth

Stratospheric Aerosol Geoengineering (SAG) is one of the solar geoengineering approaches that have been proposed to offset some of the impacts of anthropogenic climate change. Past studies have shown that SAG may have adverse impacts on the global hydrological cycle. Using a climate model, we quantify the sensitivity of the tropical monsoon precipitation to the meridional distribution of volcanic sulfate aerosols prescribed in the stratosphere in terms of the changes in aerosol optical depth (AOD). In our experiments, large changes in summer monsoon precipitation in the tropical monsoon regions are simulated, especially over the Indian region, in association with meridional shifts in the location of the intertropical convergence zone (ITCZ) caused by changes in interhemispheric AOD differences. Based on our simulations, we estimate a sensitivity of − 1.8° ± 0.0° meridional shift in global mean ITCZ and a 6.9 ± 0.4% reduction in northern hemisphere (NH) monsoon index (NHMI; summer monsoon precipitation over NH monsoon regions) per 0.1 interhemispheric AOD difference (NH minus southern hemisphere). We also quantify this sensitivity in terms of interhemispheric differences in effective radiative forcing and interhemispheric temperature differences: 3.5 ± 0.3% change in NHMI per unit (Wm−2) interhemispheric radiative forcing difference and 5.9 ± 0.4% change per unit (°C) interhemispheric temperature difference. Similar sensitivity estimates are also made for the Indian monsoon precipitation. The establishment of the relationship between interhemispheric AOD (or radiative forcing) differences and ITCZ shift as discussed in this paper will further facilitate and simplify our understanding of the effects of SAG on tropical monsoon rainfall.

Analysis of Himalayan summer monsoon rainfall characteristics using Indian High‐Resolution Regional Reanalysis

AbstractThis study assesses the high‐resolution Indian Monsoon Data Assimilation and Analysis (IMDAA) dataset in representing the Indian summer monsoon (ISM) precipitation over the Himalayan region against ground‐based gridded (IMD), satellite‐based (TRMM, GPM‐IMERG and CHIRPS) and ERA5 reanalysis datasets at seasonal mean, trends, interannual and diurnal timescales. We first evaluate the relative performance of IMDAA rainfall using various statistical performance measures against the aforementioned datasets. Analysis suggests that IMDAA successfully captures the spatial distribution of ISM mean precipitation and seasonal cycle of daily rainfall over the Himalayas as in gridded, satellite and ERA5 reanalysis datasets, albeit with some overestimation in magnitude. Furthermore, statistical results show that IMDAA exhibits a wetter tendency, more RMSE, and higher precipitation variations over the foothills of the Himalayas. The results of the skill score determine that IMDAA diligently captured moderate and extreme precipitation events but was unable to detect heavy and low‐precipitation events. Our analysis further reveals that IMDAA shows a positive trend in mean ISM precipitation over the western Himalayan region, in line with CHIRPS, IMERG, IMD, ERA5 and TRMM datasets. Investigation of rainfall trends from station observations over the foothills of the Himalayas revealed mixed trends, with some stations (Tehri, Uttarkashi and Mukhim) showing an increasing trend and others (Dunta and Bhatwari) showing a decreasing trend. However, IMDAA reanalysis agrees well with all gauge station‐based trends. Additionally, the interannual variability of Himalayan precipitation is well represented in IMDAA as its principal component correlates well with its seasonal precipitation anomalies. It is found that the leading empirical orthogonal function mode of IMDAA accounts 24% of the total variance, demonstrating a single mode of variability. Furthermore, it is noticeable that strong convective activity during wet ISM years than in dry years, suggesting that the IMDAA can capture these variations successfully compared to ERA5. The interannual variability of ISM precipitation over the Himalayas is strongly associated with the El Niño–Southern Oscillation, which is well represented by IMDAA. In addition, IMDAA successfully replicated the diurnal cycle of precipitation over the central Himalayas, showing the presence of bimodal precipitation maxima: one in the afternoon and another one in the early morning, which is consistent with satellite observations. Thus, our results suggest that the IMDAA is a valuable dataset to understand the spatial–temporal pattern of summer precipitation over such a complex high mountain Asian region.

South-West and North-East Monsoon Precipitations Bright Band Characteristics over Kadapa, Semi-arid Regions of India

bstract: Long-term (3-yrs) observation of precipitation during Southwest (SW) and Northeast (NE) With and without Bright Band/melting layer using a Micro Rain Radar (MRR) is investigated. Profiles of DSD in Bright Band (BB) and Non-Bright Band (NBB) cases demonstrate that the BB rain events are associated with higher number concentration of larger drops and NBB events are associated with higher concentration of smaller drops.

Changes in the West Africa Monsoon Precipitation Extremes during ENSO developing Phases

ABSTRACT A 37-year record of rainfall gridded data covering West Africa and a Global Sea Surface Temperature (SST) dataset are used to investigate the remote influence of SST anomalies in the Equatorial Pacific on the interannual variability of West Africa’s extreme rainfall indices over the period 1981–2018. The top five (5) years with the strongest and weakest peak of Niño3.4 SST monthly anomalies are selected, and May-to-September (MJJAS) composite anomalies of the total and extreme rainfall indices are performed. Results reveal that Equatorial Pacific SST’s impacts on daily rainfall intensity are generally more robust than that on their frequency. The significant changes in the mean zonal atmospheric circulation associated with the SST lead to significant dynamic and thermodynamic changes that affect the West African monsoon system locally. During El Niño (La Niña) years, (i) a weakening (strengthening) of the Tropical Easterly Jet (TEJ), (ii) a strengthening (weakening), and southward (northward) shift position of the African Easterly Jet (AEJ), and (iii) a decrease (increase) of the monsoon flow are noted. These changes in the atmospheric circulation prevent (encourage) a supply of moisture, resulting in a reduction (increase) in extreme precipitation observed across West Africa. Equatorial eastern Pacific warming (cooling) is also shown to lead to stable (unstable) atmospheric conditions over West Africa that block (generate) the development of convective systems.

Sediment delivery to sustain the Ganges-Brahmaputra delta under climate change and anthropogenic impacts

The principal nature-based solution for offsetting relative sea-level rise in the Ganges-Brahmaputra delta is the unabated delivery, dispersal, and deposition of the rivers’ ~1 billion-tonne annual sediment load. Recent hydrological transport modeling suggests that strengthening monsoon precipitation in the 21st century could increase this sediment delivery 34-60%; yet other studies demonstrate that sediment could decline 15-80% if planned dams and river diversions are fully implemented. We validate these modeled ranges by developing a comprehensive field-based sediment budget that quantifies the supply of Ganges-Brahmaputra river sediment under varying Holocene climate conditions. Our data reveal natural responses in sediment supply comparable to previously modeled results and suggest that increased sediment delivery may be capable of offsetting accelerated sea-level rise. This prospect for a naturally sustained Ganges-Brahmaputra delta presents possibilities beyond the dystopian future often posed for this system, but the implementation of currently proposed dams and diversions would preclude such opportunities.

Seasonal water source patterns in a northern Arizona pine forest

The relationships among stand density and seasonal plant water source patterns in ponderosa pine (Pinus ponderosa) forests are important for informed management decisions in a bimodal climate with increasing variability in winter and monsoon precipitation inputs. Winter precipitation recharges soil moisture, yet it has declined over the past 20 years in the southwestern United States, and monsoon precipitation is becoming more variable in both magnitude and timing. Near Flagstaff, Arizona in August 2013 (monsoon), October 2013 (post-monsoon), and May 2014 (post winter snow melt), we measured soil moisture, soil water δD at five depths, and xylem water δD in Muhlenbergia montana (a perennial C4 grass), Festuca arizonica (a perennial C3 grass), and P. ponderosa seedlings (< 2 years old), saplings (2–5 cm basal diameter), and mature trees (> 60 cm diameter at breast height) in treated (thinned and burned) and untreated (no thinning, no burning) stands. We found that soil moisture was higher at all soil depths in treated stands in May, after snow melt, and this pattern persisted through August in the deepest soil (60 cm). We also found that, in all sampling months, δD in xylem water of grasses and pine seedlings indicated use of shallower soil water than for pine saplings and mature trees, presumably due to differences in rooting depths. Additionally, in August, δD in xylem water of pine saplings and mature trees indicated greater reliance on a deeper water source in untreated stands than in treated stands, likely due to greater competition for shallow water in untreated stands. Our isotopic data indicate that grasses and seedlings used predominantly monsoon water in August and October, while pine saplings and mature trees used predominantly winter water during all sampling months. Importantly, our data indicate that regenerating trees (seedlings and saplings) used both winter and monsoon seasonal water sources, suggesting an increasingly important role for monsoon precipitation if winter precipitation inputs continue to decline. Collectively, these findings demonstrate that management actions can benefit forests via increased soil moisture, that overstory trees rely predominantly on winter precipitation, and that monsoon precipitation is important for herbaceous species and younger, regenerating overstory trees.

Estimating the response of Himalayan old-growth mountain forests to decreased monsoon precipitation

Forests in the Himalayas are a major carbon store, but are under threat due to changes in precipitation regime. To simulate a precipitation decline, throughfall-exclusion (TFE) shelters were applied during three consecutive monsoon seasons in an oak forest (2.650 m a.s.l.) and a conifer-dominated forest (3.260 m a.s.l.) in central Bhutan. Leaf water potentials, tree mortality, stem increment, soil CO2 efflux, litterfall and fine root dynamics were assessed. TFE significantly and consistently decreased topsoil (0–30 cm) moisture and leaf water potentials of Quercus lanata and Quercus griffithii (lower elevation), and to a lesser extend those of Tsuga dumosa and Quercus semecarpifolia, (higher elevation). TFE did not impose tree mortality. Stem increment remained unaffected until the second TFE year, but showed reductions during the third year with Tsuga dumosa being most severely affected (-60%). Standing fine root biomass stocks were hardly affected by TFE. Increased root necromass and faster fine root growth in the lower elevation forest suggest that the oak trees increased C allocation below ground. Soil CO2 efflux sharply declined during all three TFE years in both forests. Above ground litter input was unaffected by TFE until the second treatment year. Overall, both forest ecosystems appeared highly resistant to the imposed soil drying, with no signs of tree mortality and stable living root biomass stocks.

Asymmetric Boreal Summer Intraseasonal Oscillation Events over the Western North Pacific and Their Impacts on East Asian Precipitation

Abstract The boreal summer intraseasonal oscillation (BSISO) is the most prominent tropical subseasonal signature. Due to the restriction of methodology used to extract BSISO, most of the previous studies ignored its asymmetry. This study reexamines the BSISO events over the western North Pacific (WNP) for 1985–2010 with a hierarchical cluster analysis. Two categories of BSISO events are classified, the long-period (20–60 day) and short-period (10–20 day) events. The long-period BSISO events manifest as a northward-propagating mode with a significant phase asymmetry characterized by a fast development, but a slow decay of the intraseasonal convection. The phase asymmetry is found to be determined by the BSISO-induced amplitude-asymmetric sea surface temperature (SST) anomalies, in which the suppressed convection-induced positive SST anomalies are stronger than the active convection-induced negative ones. Such amplitude-asymmetric SST anomalies result from the nonlinear relationship between convection and surface downward shortwave radiation flux anomalies caused by the cloud transmission effect. The stronger positive SST anomalies–induced turbulence flux anomalies act as a negative feedback onto the atmosphere, making the transition from the convection suppressed phase to the active phase earlier and faster. The fast-developing convection tends to cause a fast northeastward retreat of the preceding enhanced western North Pacific subtropical high. Accordingly, the middle and lower reaches of Yangtze River valley experience a rapid reversal from the increased precipitation to the decreased. The asymmetric BSISO events over WNP and their impacts revealed in this study would provide a new potential for subseasonal-to-seasonal forecast of the East Asian summer monsoon precipitation.

Diverse skill of seasonal dynamical models in forecasting South Asian monsoon precipitation and the influence of ENSO and IOD

The South Asia Seasonal Climate Outlook Forum (SASCOF) issues seasonal tercile precipitation forecasts to provide advance warning of anomalously dry or wet monsoon seasons in South Asia. To increase objectivity of the SASCOF seasonal outlook, the World Meteorological Organisation recommends using a multi-model ensemble combining the most skilful dynamical seasonal models for the region. We assess the skill of 12 dynamical models at forecasting seasonal precipitation totals for 1993–2016 for the southwest (June–July–August–September) and northeast (October–November–December) monsoon seasons at regional and national levels for Afghanistan, Bangladesh, Nepal, and Pakistan, using identical forecast periods, hindcast initialisation months and domain used at the SASCOF. All models demonstrate positive skill when regionally-averaged, especially for the southwest monsoon season, noting considerable spatial differences. Models exhibit highest skill where correlation between observed precipitation and El Niño Southern Oscillation (ENSO) is highest, e.g., central/north India and Nepal during the southwest monsoon, and Afghanistan and north Pakistan during the northeast monsoon. Model skill is especially low in northwest India and northeast of South Asia during the southwest monsoon, e.g., Bangladesh (despite high precipitation totals) coinciding with a weak ENSO teleconnection. The Indian Ocean Dipole teleconnection is less pronounced in the southwest monsoon season, whereas the spatial pattern for the northeast monsoon closely resembles that of ENSO. Due to high variability in model skill, we recommend basing the SASCOF forecast on a multi-model ensemble of all models but discounting poorly performing models at the national level.

Middle Pleistocene re-organization of Australian Monsoon

The sensitivity of the Australian Monsoon to changing climate boundary conditions remains controversial due to limited understanding of forcing processes and past variability. Here, we reconstruct austral summer monsoonal discharge and wind-driven winter productivity across the Middle Pleistocene Transition (MPT) in a sediment sequence drilled off NW Australia. We show that monsoonal precipitation and runoff primarily responded to precessional insolation forcing until ~0.95 Ma, but exhibited heightened sensitivity to ice volume and pCO2 related feedbacks following intensification of glacial-interglacial cycles. Our records further suggest that summer monsoon variability at the precessional band was closely tied to the thermal evolution of the Indo-Pacific Warm Pool and strength of the Walker circulation over the past ~1.6 Myr. By contrast, productivity proxy records consistently tracked glacial-interglacial variability, reflecting changing rhythms in polar ice fluctuations and Hadley circulation strength. We conclude that the Australian Monsoon underwent a major re-organization across the MPT and that extratropical feedbacks were instrumental in driving short- and long-term variability.

Chironomid (Insecta: Chironomidae) community structure response to hydrological changes in the mid‐1950s in lake Nam Co, Tibetan Plateau

ABSTRACTThe recent rise in air temperatures detected at high altitudes of the Tibetan Plateau has accelerated glacier melt and retreat. Moreover, enhanced monsoonal precipitation has increased runoff and transport of allochthonous material to the lakes. Consequently, water levels are rising, modifying the spatial distribution and composition of local aquatic biota. To infer these environmental and biological changes in recent decades, a 30‐cm‐long sediment core, representing the past ~160 years, from Nam Co, an endorheic lake, was analyzed for subfossil chironomid assemblages and sediment geochemistry. In total, 25 chironomid morphotypes were identified. Nineteen were considered as non‐rare taxa (abundances ≥2%) and six as rare taxa (abundances <2%). Since 1956 ce, higher chironomid richness (S = 19) is evident compared to the previous 100 years. The simultaneous decrease in the abundance of profundal Micropsectra radialis‐type and increase of both Chironomus and Procladius, taxa adapted to more eurytopic and slightly warmer water bodies, indicate increasing water temperatures and intensified primary productivity. The dominance of littoral chironomid assemblages reflects increasing lake water levels, flooded shorelines and expansion of littoral areas driven by increased precipitation and glacial meltwater input both resulting from the increase in air temperatures. This scenario is confirmed by increases in total nitrogen and Zr/Rb ratios, indicating higher productivity and coarser grain size as a consequence of increased runoff via the Niya Qu. These hydrological changes have resulted in a positive water balance that can be linked to an increase in moisture supply from the Indian summer monsoon and glacier melt, reflecting increasing temperatures and precipitation since 1956 ce, ultimately driven by anthropogenic warming.

The importance of monsoon precipitation for foundation tree species across the semiarid Southwestern U.S.

Forest dynamics in arid and semiarid regions are sensitive to water availability, which is becoming increasingly scarce as global climate changes. The timing and magnitude of precipitation in the semiarid southwestern U.S. (“Southwest”) has changed since the 21st century began. The region is projected to become hotter and drier as the century proceeds, with implications for carbon storage, pest outbreaks, and wildfire resilience. Our goal was to quantify the importance of summer monsoon precipitation for forested ecosystems across this region. We developed an isotope mixing model in a Bayesian framework to characterize summer (monsoon) precipitation soil water recharge and water use by three foundation tree species (Populus tremuloides [aspen], Pinus edulis [piñon], and Juniperus osteosperma [Utah juniper]). In 2016, soil depths recharged by monsoon precipitation and tree reliance on monsoon moisture varied across the Southwest with clear differences between species. Monsoon precipitation recharged soil at piñon-juniper (PJ) and aspen sites to depths of at least 60 cm. All trees in the study relied primarily on intermediate to deep (10-60 cm) moisture both before and after the onset of the monsoon. Though trees continued to primarily rely on intermediate to deep moisture after the monsoon, all species increased reliance on shallow soil moisture to varying degrees. Aspens increased reliance on shallow soil moisture by 13% to 20%. Utah junipers and co-dominant ñons increased their reliance on shallow soil moisture by about 6% to 12%. Nonetheless, approximately half of the post-monsoon moisture in sampled piñon (38-58%) and juniper (47-53%) stems could be attributed to the monsoon. The monsoon contributed lower amounts to aspen stem water (24-45%) across the study area with the largest impacts at sites with recent precipitation. Therefore, monsoon precipitation is a key driver of growing season moisture that semiarid forests rely on across the Southwest. This monsoon reliance is of critical importance now more than ever as higher global temperatures lead to an increasingly unpredictable and weaker North American Monsoon.

Signatures of aerosol-induced decline in evapotranspiration over the Indo-Gangetic Plain during the recent decades

Evapotranspiration (ET) is the primary process of water transfer in the hydrological cycle over land and is linked to water, energy and carbon cycles. While the global hydrological cycle is expected to intensify in a warming climate with enhanced ET and precipitation, the magnitude and spatial distribution of regional scale response of ET to climate change remains uncertain. Here we present an analysis of in-situ observations of ET from 23 stations in India during 1979-2008, which shows that the annual ET has declined by about 9% over the humid sub-regions of the Indo-Gangetic Plain (IGP). Additional analysis from high-resolution climate model simulations and observed climate datasets lend support to the role of aerosol-induced solar-dimming in intensifying ET reductions, in a background of decreasing monsoon precipitation and soil-moisture levels, over the IGP

How accurate are infrared-only and rain gauge-adjusted multi-satellite precipitation products in the southwest monsoon precipitation estimation across India?

A dense network of rain gauges and considerably large variability of the southwest monsoon precipitation across the country make India a suitable test-bed to evaluate any satellite-based precipitation product. In this paper, three real-time infrared-only precipitation products derived from the INSAT-3D satellite namely, INSAT Multispectral Rainfall (IMR), Corrected IMR (IMC) and Hydro-Estimator (HEM) and three rain gauge-adjusted Global Precipitation Measurement (GPM)-based multi-satellite precipitation products namely, Integrated Multi-satellitE Retrievals for GPM (IMERG), Global Satellite Mapping of Precipitation (GSMaP) and an Indian merged satellite-gauge product (INMSG) have been evaluated over India at a daily timescale for the southwest monsoon seasons of 2020 and 2021. An evaluation against rain gauge-based gridded reference dataset shows noticeable reduction of bias in IMC product over IMR, primarily over the orographic regions. However, INSAT-3D infrared-only precipitation retrieval algorithms have limitations in shallow and convective precipitation estimation. Among rain gauge-adjusted multi-satellite products, INMSG is shown to be the best product in the monsoon precipitation estimation over India due to use of rather larger number of rain gauges than IMERG and GSMaP products. All satellite-derived precipitation products, i.e. infrared-only and gauge-adjusted multi-satellite products underestimate heavy monsoon precipitation by 50-70%. The bias decomposition analysis indicates that a simple statistical bias correction would considerably improve the performance of the INSAT-3D precipitation products over the central India, but the same might not work over the west coast due to rather larger contributions of both positive and negative hit bias components. Although rain gauge-adjusted multi-satellite precipitation products show very small or negligible total biases in the monsoon precipitation estimation, positive and negative hit bias components are considerable over the west coast and central India. Furthermore, rain gauge-adjusted multi-satellite precipitation products underestimate very heavy to extremely heavy precipitation with larger magnitudes than the INSAT-3D derived precipitation products over the central India. Among the rain gauge-adjusted multi-satellite precipitation products, INMSG has smaller bias and error than IMERG and GSMaP products for very heavy to extremely heavy monsoon precipitation over the west coast and central India. Preliminary results of this study would be useful for end users in choosing a better precipitation product for real-time and research applications as well as for algorithm developers in further improving these products.

How does the explicit treatment of convection alter the precipitation–soil hydrology interaction in the mid-Holocene African humid period?

Abstract. Global climate models with coarse horizontal resolution are largely unable to reproduce the monsoonal precipitation pattern over North Africa during the mid-Holocene. Here we present the first regional, storm-resolving simulations with an idealized but reasonable mid-Holocene vegetation cover. In these simulations, the West African monsoon expands farther north by about 4–5∘, and the precipitation gradient between the Guinea coast and the Sahara decreases compared to simulations with a barren Sahara as it is today. The northward shift of monsoonal precipitation is caused by land surface–atmosphere interaction, i.e., the coupling of soil moisture and precipitation, as well as interactions of the land surface with the large-scale monsoon circulation (e.g., the African easterly jet). The response of the monsoon circulation to an increased vegetation cover is qualitatively similar but more pronounced in parameterized convection simulations. We attribute the differences in monsoonal precipitation to differences in soil moisture that are strongly controlled by runoff and precipitation characteristics. If precipitation is intense and falls over a spatially small region, as in our storm-resolving simulations, about 35 % of all precipitation water goes into runoff instead of filling soil moisture storage. In contrast, in light and spatially more homogeneous precipitation, as produced in our parameterized convection simulations, only some 20 % leaves the grid cell as runoff. Therefore, much more water is available to maintain high soil moisture content. We confirm the significant role of soil moisture and runoff by performing simulations with the same constant soil moisture field in both storm-resolving and parameterized convection simulations. These constant soil moisture simulations cancel the effect of lower soil moisture on the land–atmosphere feedback cycle in our storm-resolving simulations. We show that precipitation strongly increases in the storm-resolving simulations, especially in moisture-controlled regions, such as the northern Sahel and Sahara, and reaches equally high values as in parameterized convection simulations. Our study highlights how the type of rainfall (e.g., local and intense or widespread and light) impacts soil moisture and thus land–atmosphere feedbacks. This is contrary to many studies that focus mainly on the amount of rainfall and how it modifies land–atmosphere feedbacks. Moreover, this study suggests that comprehensive land-surface schemes, which appropriately respond to varying precipitation characteristics, are needed for studying land surface–atmosphere interaction.

Possible influence of the interdecadal variation of the extratropical southern Indian Ocean SST on East Asian summer monsoon precipitation

Observations indicate that East Asian summer precipitation exhibits significant interdecadal variability, with an alternating reverse phase distribution of rainfall from south to north, which is different from the consistent increase or decrease of precipitation in the whole region. The East Asian summer monsoon mainly affects the spatial pattern of meridional tripole precipitation on the interdecadal timescale. Moreover, the interdecadal sea surface temperature variability in the extratropical southern Indian Ocean is the most significant in the boreal summer. When there is anomalous warming in the extratropical southern Indian Ocean, the Somali cross-equatorial flow weakens and then alternating positive and negative waves propagate to central East Asia. In contrast, the New Guinea cross-equatorial flow experiences interdecadal enhancement with cyclonic circulation anomalies over the Northwest Pacific and anticyclonic circulation anomalies over the Philippines, which leads to a weakening of the South China Sea monsoon trough. On one hand, the cyclonic-anticyclonic coupling over the Philippines and Northwest Pacific results in an anomalous eastward transport of water vapor and reduced water vapor input over southern East Asia. On the other hand, the coupling strengthens the water vapor transport from the mid-latitude Northwest Pacific to central East Asia. These circulation anomalies favor the development of a meridional tripole pattern, i.e. a “negative – positive – negative” pattern of East Asian summer monsoon precipitation anomalies on the interdecadal timescale, which is specifically manifested in the abnormal increase of precipitation in central East Asia and the decrease of precipitation in northern and southern East Asia.