Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.2.2 Wet and Dry ====

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'''Mean precipitation:''' The most prominent features about changes in precipitation over Asia (1901–2010) are the increasing precipitation trends across higher latitudes, along with some scattered smaller regions of detectable increases and decreases ( [[#Knutson--2018|Knutson and Zeng, 2018]] ); however, spatial variability remains high (W. [[#Wang--2015|]] [[#Wang--2015|Wang et al., 2015]] ; [[#Limsakul--2016|Limsakul and Singhruck, 2016]] ; [[#Supari--2017|Supari et al., 2017]] ; [[#Rahimi--2018|Rahimi et al., 2018]] , 2019; [[#Sein--2018|Sein et al., 2018]] ; [[#Kumar--2019|Kumar et al., 2019]] ; H. [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|Wang et al., 2019]] ; see Atlas.5) ( ''medium confidence'' ).

Mean precipitation is ''likely'' to increase in most areas of northern (WSB, ESB, RFE), southern (ECA, TIB, SAS) and East Asia (EAS) in different scenarios ( ''high confidence'' ) ( [[#Huang--2014|Huang et al., 2014]] ; [[#Xu--2017|Xu et al., 2017]] ; [[#Kusunoki--2018|Kusunoki, 2018]] ; [[#Mandapaka--2018|Mandapaka and Lo, 2018]] ; [[#Luo--2019|Luo et al., 2019]] ; [[#Wu--2019|Wu et al., 2019]] ; X. [[#Zhu--2019|]] [[#Zhu--2019|Zhu et al., 2019]] ; [[#Almazroui--2020|Almazroui et al., 2020]] ; [[#Jiang--2020|Jiang et al., 2020]] ; [[#Rai--2020|Rai et al., 2020]] ; see Atlas.5). Monsoon circulation will also increase seasonal contrasts, with SAS seeing wetter wet seasons and drier dry seasons (Atlas.5.3). Higher uncertainty between CMIP5 and CMIP6 as well as spatial differences lend ''low confidence'' to model projections in ARP and WCA (Atlas.5.5), with large seasonal differences ( [[#Zhu--2020|Zhu et al., 2020]] ) and some models projecting decreases in precipitation in Central Asia ( [[#Ozturk--2017|Ozturk et al., 2017]] ), Pakistan ( [[#Nabeel--2020|Nabeel and Athar, 2020]] ) and SEA (Supari et al., 2020).

'''River flood:''' Flood risk has grown in many places in China from 1961 to 2017 ( [[#Kundzewicz--2019|Kundzewicz et al., 2019]] ) ( ''low confidence'' ). In SAS, the numbers of flood events and human fatalities have increased in India during 1978–2006 ( [[#Singh--2013|Singh and Kumar, 2013]] ), whereas the average country-wide inundation depth has been decreasing during 2002–2010 in Bangladesh, attributed to improved flood management ( ''low confidence'' ) ( [[#Sciance--2018|Sciance and Nooner, 2018]] ).

Given the increase of heavy precipitation in most Asian regions, the river flood frequency and intensities will change consequently in Asia. Over China floods will increase with different levels under different warming scenarios ( ''medium confidence'' ) ( [[#Lin--2018|Lin et al., 2018]] ; [[#Kundzewicz--2019|Kundzewicz et al., 2019]] ; [[#Liang--2019|Liang et al., 2019]] ; [[#Gu--2020|Gu et al., 2020]] ). Monsoon floods will be more intense in SAS ( ''medium confidence'' ) ( [[#Nowreen--2015|Nowreen et al., 2015]] ; [[#Babur--2016|Babur et al., 2016]] ; [[#Mohammed--2018|Mohammed et al., 2018]] ). The total flood damage will increase greatly in river basins in SEA countries under the conditions of climate change and rapid urbanization in the near future ( [[#Dahal--2018|Dahal et al., 2018]] ; [[#Kefi--2020|Kefi et al., 2020]] ). A changing snowmelt regime in the mountains may contribute to a shift of spring floods to earlier periods in Central Asia in future ( ''medium confidence'' ) ( [[#Reyer--2017b|Reyer et al., 2017b]] ). The annual maximum river discharge can almost double by the mid-21st century in major Siberian rivers, and annual maximum flood area is projected to increase across Siberia mostly by 2–5% relative to the baseline period (1990–1999) under RCP8.5 scenario ( ''medium confidence'' ) ( [[#Shkolnik--2018|Shkolnik et al., 2018]] ).

'''Heavy precipitation and pluvial flood:''' Pluvial floods are driven by extreme precipitation and land use. Observed changes in extreme precipitation vary considerably by region (Chapter 11). Heavy precipitation is ''very'' ''likely'' to become more intense and frequent in all areas of Asia except in ARP ( ''medium confidence'' ) for a 2°C GWL or higher (Chapter 11).

'''Landslide:''' The majority of non-seismic fatal landslide events were triggered by rainfall, and Asia is the dominant geographical area of landslide distribution ( [[#Froude--2018|Froude and Petley, 2018]] ). Floods and landslides are the most frequently occurring natural hazards in the eastern Himalayas and hilly regions, particularly caused by torrential rain during the monsoon season ( [[#Gaire--2015|Gaire et al., 2015]] ; [[#Syed--2016|Syed and Al Amin, 2016]] ). They accounted for nearly half of the events recorded in the countries of the HKH region ( [[#Vaidya--2019|Vaidya et al., 2019]] ). Intense monsoon rainfall in northern India and western Nepal in 2013, which led to landslides and one of the worst floods in history, has been linked to increased loading of GHG and aerosols ( [[#Cho--2016|Cho et al., 2016]] ). Due to an increase of heavy precipitation and permafrost thawing, an increase in landslides is expected in some areas of Asia, such as northern Taiwan (China), some South Korean mountains, Himalayan mountains, and permafrost territories of Siberia, and the increase is expected to be the greatest over areas covered by current glaciers and glacial lakes ( ''medium confidence'' , ''medium evidence'' ) ( [[#Kim--2015|Kim et al., 2015]] ; [[#Kharuk--2016|Kharuk et al., 2016]] ; C.-W. [[#Chen--2019|]] [[#Chen--2019|Chen et al., 2019]] ; [[#Kirschbaum--2020|Kirschbaum et al., 2020]] ).

'''Aridity:''' Aridity in West Central Asia and parts of South Asia increased in recent decades ( ''medium confidence'' ), as documented in Afghanistan ( [[#Qutbudin--2019|Qutbudin et al., 2019]] ), Iran ( [[#Zarei--2016|Zarei et al., 2016]] ; [[#Zolfaghari--2016|Zolfaghari et al., 2016]] ; [[#Pour--2020|Pour et al., 2020]] ), most parts of Pakistan (K. [[#Ahmed--2018|Ahmed et al., 2018]] , 2019), and many parts of India ( [[#Roxy--2015|Roxy et al., 2015]] ; [[#Mallya--2016|Mallya et al., 2016]] ; [[#Matin--2017|Matin and Behera, 2017]] ; [[#Ramarao--2019|Ramarao et al., 2019]] ). Some spatial and seasonal differences within these regions remain, with [[#Ambika--2020|Ambika and]] [[#Mishra--2020|Mishra (2020)]] noting significant aridity declines over the Indo–Gangetic Plain in India during 1979–2018 due in part to the effect of irrigation, and [[#Araghi--2018|Araghi et al. (2018)]] found that many parts of Iran show no significant trends in aridity. There was a drying tendency in the dry season and significant wetting in the wet season in the Philippines during 1951–2010 ( [[#Villafuerte--2014|Villafuerte et al., 2014]] ), and slight wetting in Vietnam during 1980–2017 ( [[#Stojanovic--2020|Stojanovic et al., 2020]] ) ( ''low confidence'' ). In EAS there is ''low confidence'' of broad aridity changes, as the frequency of droughts have increased (especially in spring) along a strip extending from south-west China to the western part of north-east China; however, there is no evidence of a significant increase in drought severity over China as a whole and many parts in the arid north-west China got wetter during 1961–2012 (W. [[#Wang--2015|]] [[#Wang--2015|Wang et al., 2015]] ; [[#Zhai--2017|Zhai et al., 2017]] ; H. [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|Wang et al., 2019]] ; [[#Zhang--2019|Zhang and Shen, 2019]] ). In Siberia, the number of dry days has decreased for much of the region, but increased in its southern parts ( [[#Khlebnikova--2019a|Khlebnikova et al., 2019a]] ).

The counteracting factors of projected increases in precipitation and temperature across most of Asia ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] and Atlas.5) leads to ''low confidence'' ( ''limited evidence'' , inconsistent trends) for broad, long-term aridity changes with ''medium confidence'' only for aridity increases in West Central Asia and East Asia. A growing number of studies highlight the potential for more localized aridity trends, including projection ensembles indicating significant increase in aridity and more frequent and intense droughts in most parts of China (Y. [[#Li--2019|]] [[#Li--2019|Li et al., 2019]] ; [[#Yao--2020|Yao et al., 2020]] ) and India under RCP4.5 and RCP8.5 for the 2020–2100 period ( [[#Gupta--2018|Gupta and Jain, 2018]] ; [[#Bisht--2019|Bisht et al., 2019]] ; [[#Preethi--2019|Preethi et al., 2019]] ).

'''Hydrological drought:''' Section 11.9 indicates that ''limited evidence'' and inconsistent regional trends gives ''low confidence'' to observed and projected changes in hydrological drought in all Asian regions at a 2°C GWL (approximately mid-century), although West Central Asia hydrological droughts increase at the 4°C GWL (approximately end-of-century under higher emissions scenarios) ( ''medium confidence'' ). Human activities such as reservoir operation and water abstraction have had a profound effect on low river flow characteristics and drought impacts in many Asian regions ( [[#Kazemzadeh--2016|Kazemzadeh and Malekian, 2016]] ; [[#Yang--2020b|Yang et al., 2020b]] ). There was no observed overall long-term change of both meteorological droughts and hydrological droughts over India during 1870–2018 ( [[#Mishra--2020|Mishra, 2020]] ), but there were strong trends towards drying of soil moisture in north-central India ( [[#Ganeshi--2020|Ganeshi et al., 2020]] ) and intensified droughts in north-west India, parts of Peninsular India, and Myanmar ( [[#Malik--2016|Malik et al., 2016]] ). The frequency of water scarcity connected with hydrological droughts has increased significantly in southern Russia since the beginning of the 21st century ( [[#Frolova--2017|Frolova et al., 2017]] ). Higher future temperatures are expected to alter the seasonal profile of hydrologic droughts given reduced summer snowmelt ( ''medium confidence'' ) downstream of mountains such as the Himalayas and the Tibetan Plateau ( [[#Sorg--2014|Sorg et al., 2014]] ). Several studies project more severe future hydrological drought in the Weihe River basin in northern China ( [[#Yuan--2016|Yuan et al., 2016]] ; [[#Sun--2020|Sun and Zhou, 2020]] ).

'''Agricultural and ecological drought:''' Section 11.9 assesses ''medium confidence'' in observed increases to agricultural and ecological droughts in West Central Asia, East Central Asia, and East Asia. Persistent droughts were the main factor for grassland degradation and desertification in Central Asia in the early 21st century (G. [[#Zhang--2018|]] [[#Zhang--2018|Zhang et al., 2018]] ; [[#Emadodin--2019|Emadodin et al., 2019]] ). Compound meteorological drought and heat events, which lead to water stress conditions for agricultural and ecological systems, have become more frequent, widespread and persistent in China especially since the late 1990s ( [[#Yu--2020|Yu and Zhai, 2020]] ). There were more agricultural droughts in northern China than in southern China, and the intensity of agricultural drought increased during 1951–2018 ( [[#Zhao--2021|Zhao et al., 2021]] ).

Studies examining a 2°C GWL give ''low confidence'' for projected broad changes to agricultural and ecological drought across all Asia regions, although at 4°C GWL agricultural and ecological drought increases are projected for West Central Asia and East Asia along with a decrease in South Asia ( ''medium confidence'' ) ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ). Summer temperature increase will enhance evapotranspiration, facilitating ecological and agricultural drought over Central Asia towards the latter half of this century (Chapter 11; see also Figure 12.4 for soil moisture and DF indices; [[#Ozturk--2017|Ozturk et al., 2017]] ; [[#Reyer--2017b|Reyer et al., 2017b]] ; [[#Senatore--2019|Senatore et al., 2019]] ). However, broader changes in droughts could not be determined in Asia due to the mixture of total precipitation signals together with temperature increase patterns ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] and Atlas.5).

'''Fire weather:''' Under the global warming scenario of 2°C, the magnitude of length and frequency of fire seasons are projected to increase with strong effects in India, China and Russia ( ''medium confidence'' ) (Q. [[#Sun--2019|]] [[#Sun--2019|]] [[#Sun--2019|Sun et al., 2019]] ). [[#Abatzoglou--2019|Abatzoglou et al. (2019)]] found that higher fire weather conditions due to climate change emerge in the first part of the 21st century in South China, WCA as well as in boreal areas of Siberia and RFE. The potential burned areas in five Central Asian countries (Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan and Turkmenistan) will increase by 2–8% in the 2030s and 3–13% in the 2080s compared with the baseline ( ''medium confidence'' ) (1971–2000; [[#Zong--2020|Zong et al., 2020]] ).

'''In conclusion, there is''' medium confidence '''that extreme precipitation, mean precipitation and river floods will increase across most Asian regions. There is''' low confidence '''for projected changes in aridity and drought given overall increases in precipitation and regional inconsistencies, with medium increases for West Central Asia and East Asia especially beyond the middle of the century and global warming levels beyond 2°C. Fire weather seasons are projected to lengthen and intensify particularly in the northern regions''' ( medium confidence ''').'''

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