Failure of CMIP5 climate models in simulating post‐1950 decreasing trend of Indian monsoon

Saha, Anamitra; Ghosh, Subimal; Sahana, A. S.; Rao, E. P.

doi:10.1002/2014gl061573

Cited by 170 publications

(128 citation statements)

References 38 publications

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“…Various authors have questioned the ability of CMIP5 models to capture observed monsoon rainfall trends over India (e.g. Saha et al, 2014) and therefore the reliability of CMIP5 at making projections of future monsoon rainfall (Ramesh and Goswami, 2014;Sabeerali et al, 2014). In our study we shall demonstrate that it is only when aerosol indirect effects are included, and therefore when more physical processes are being represented, that these models are able to capture the observed trends.…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 71%

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Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

2015

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Abstract. Comparison of single-forcing varieties of 20thcentury historical experiments in a subset of models from the Fifth Coupled Model Intercomparison Project (CMIP5) reveals that South Asian summer monsoon rainfall increases towards the present day in Greenhouse Gas (GHG)-only experiments with respect to pre-industrial levels, while it decreases in anthropogenic aerosol-only experiments. Comparison of these single-forcing experiments with the all-forcings historical experiment suggests aerosol emissions have dominated South Asian monsoon rainfall trends in recent decades, especially during the 1950s to 1970s. The variations in South Asian monsoon rainfall in these experiments follows approximately the time evolution of inter-hemispheric temperature gradient over the same period, suggesting a contribution from the large-scale background state relating to the asymmetric distribution of aerosol emissions about the equator.By examining the 24 available all-forcings historical experiments, we show that models including aerosol indirect effects dominate the negative rainfall trend. Indeed, models including only the direct radiative effect of aerosol show an increase in monsoon rainfall, consistent with the dominance of increasing greenhouse gas emissions and planetary warming on monsoon rainfall in those models. For South Asia, reduced rainfall in the models with indirect effects is related to decreased evaporation at the land surface rather than from anomalies in horizontal moisture flux, suggesting the impact of indirect effects on local aerosol emissions. This is confirmed by examination of aerosol loading and cloud droplet number trends over the South Asia region. Thus, while remote aerosols and their asymmetric distribution about the equator play a role in setting the inter-hemispheric temperature distribution on which the South Asian monsoon, as one of the global monsoons, operates, the addition of indirect aerosol effects acting on very local aerosol emissions also plays a role in declining monsoon rainfall. The disparity between the response of monsoon rainfall to increasing aerosol emissions in models containing direct aerosol effects only and those also containing indirect effects needs to be urgently investigated since the suggested future decline in Asian anthropogenic aerosol emissions inherent to the representative concentration pathways (RCPs) used for future climate projection may turn out to be optimistic.In addition, both groups of models show declining rainfall over China, also relating to local aerosol mechanisms. We hypothesize that aerosol emissions over China are large enough, in the CMIP5 models, to cause declining monsoon rainfall even in the absence of indirect aerosol effects. The same is not true for India.

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Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 71%

“…poorly represented observed trends in monsoon rainfall when take as a whole (Saha et al, 2014;Sabeerali et al, 2014;Salzmann et al, 2014).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 89%

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

2015

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“…Meanwhile, the CMIP5 future projections suggest an increase in rainfall over the central Indian subcontinent 26 , though one must note the ongoing debate about whether CMIP5 models are in fact capturing the historic monsoon trends accurately 4,11,12,24 and whether the monsoon projections are reliable in these models 25 . The overall weakening trend of monsoon rainfall over South Asia is a matter of grave concern since the socio-economic livelihood in this region, including agriculture, water resources and power generation are irrevocably dependent on it.…”

Section: Discussionmentioning

confidence: 99%

Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land-sea thermal gradient

et al. 2015

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There are large uncertainties looming over the status and fate of the South Asian summer monsoon, with several studies debating whether the monsoon is weakening or strengthening in a changing climate. Our analysis using multiple observed datasets demonstrates a significant weakening trend in summer rainfall during 1901-2012 over the central-east and northern regions of India, along the Ganges-Brahmaputra-Meghna basins and the Himalayan foothills, where agriculture is still largely rain-fed. Earlier studies have suggested an increase in moisture availability and land-sea thermal gradient in the tropics due to anthropogenic warming, favouring an increase in tropical rainfall. Here we show that the land-sea thermal gradient over South Asia has been decreasing, due to rapid warming in the Indian Ocean and a relatively subdued warming over the subcontinent. Using long-term observations and coupled model experiments, we provide compelling evidence that the enhanced Indian Ocean warming potentially weakens the land-sea thermal contrast, dampens the summer monsoon Hadley circulation, and thereby reduces the rainfall over parts of South Asia.

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“…Hence, the reliability of climate model's projections for future changes in the hydrology of the region largely depends upon their realistic representation of both MPR and WPR for the present-day climate. While many studies that assess the representation of precipitation regimes in the climate models have focused on the reproducibility of the magnitude of precipitation, its geographical distribution, its temporal evolution or its extremes [7,[10][11][12][13][14], less attention has been given to the representation of the seasonal cycle and to the overall seasonality [15][16][17]. Changes in the seasonality of precipitation regimes directly affect the timings of the water availability and are related to the risks of droughts and floods [18].…”

Section: Introductionmentioning

confidence: 99%

Seasonality of Precipitation over Himalayan Watersheds in CORDEX South Asia and their Driving CMIP5 Experiments

Hasson

2016

Atmosphere

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Abstract:Since the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments exhibit limited skill in reproducing the statistical properties of prevailing precipitation regimes over the major Himalayan watersheds (Indus, Ganges, Brahmaputra and Mekong), this study evaluates the anticipated added skill of their dynamically refined simulations performed under the framework of Coordinated Regional Climate Downscaling Experiments for South Asia (CX-SA). For this, the fidelity of eight CX-SA experiments against their six driving CMIP5 experiments is assessed for the historical period in terms of time-dependent statistical properties (onset/retreat timings and rapid fractional accumulation-RFA) of the dominant summer monsoonal precipitation regime (MPR). Further, a self-defining seasonality index (SI), which is a product of precipitation and the distance of its actual distribution relative to its uniform distribution (relative entropy-RE), has been computed for MPR, westerly precipitation regime (WPR) and annual precipitation. The time evolution of precipitation, RE and SI has also been analyzed. Results suggest that CX-SA experiments simulate even higher wet biases than their driving CMIP5 experiments over all study basins, mainly due to higher wet biases simulated over the Himalayas and Tibetan Plateau. Most of the CX-SA experiments suggest unrealistic timings of the monsoon onset that are far earlier than their driving CMIP5 experiments for all basins. Generally, CX-SA experiments feature higher underestimation of RFA slope, RE and SI, distancing their driving CMIP5 experiments farther from observations. Interestingly, regardless of the diverse skill of CMIP5 experiments, their fine scale CX-SA experiments exhibit quite a similar skill when downscaled by the same regional climate model (RCM), indicating RCM's ability to considerably alter the driving datasets. These findings emphasize on improving the fidelity of simulated precipitation regimes over the Himalayan watersheds by exploiting the potential of RCMs in term of microphysics, resolutions and convective closures, and preferably, on resolving the crucial fine scale processes further down to their representative (meso-to-local) scales.

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Failure of CMIP5 climate models in simulating post‐1950 decreasing trend of Indian monsoon

Cited by 170 publications

References 38 publications

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land-sea thermal gradient

Seasonality of Precipitation over Himalayan Watersheds in CORDEX South Asia and their Driving CMIP5 Experiments

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