Changes In Precipitation With Climate Change
CLIMATE RESEARCHClim ResContribution to CR Special 25 ‘Climate services for sustainable development’Published OPENACCESSKEY WORDS: Climate change · Precipitation · Storms · Drought · Extremes · Floods · Geoengineering ·Climate modelsResale or republication not permitted without written consent of the publisher1. INTRODUCTIONHeated by the sun’s radiation, the ocean and landsurface evaporate water, which then moves aroundwith winds in the atmosphere, condenses to formclouds, and falls back to the Earth’s surface as rain orsnow, with the flow to oceans via rivers, completing theglobal hydrological (water) cycle.Precipitation varies from year to year and overdecades, and changes in amount, intensity, frequency,and type (e.g. snow vs. rain) affect the environment andsociety. Steady moderate rains soak into the soil andbenefit plants, while the same amounts of rainfall in ashort period of time may cause local flooding and runoff,leaving soils much drier at the end of the day (Fig. 1).Snow may remain on the ground for some months beforeit melts and runs off. Even with identical amounts, theclimate can be very different if the frequency and intensity of precipitation differ, as illustrated in Fig. 1, and ingeneral the climate is changing from being more likethat at Station (Stn) B in Fig. 1 than that at Stn A. Theseexamples highlight the fact that the characteristics ofprecipitation are just as vital as the amount, in termsof the effects on the soil moisture and stream flow.Hydrological extreme events are typically defined asfloods and droughts. Floods are associated with ex-*Email: trenbert@ucar.edu Inter-Research 2011 · www.int-res.comTrenberth KEABSTRACT: There is a direct influence of global warming on precipitation. Increased heating leadsto greater evaporation and thus surface drying, thereby increasing the intensity and duration ofdrought. However, the water holding capacity of air increases by about 7% per 1 C warming, whichleads to increased water vapor in the atmosphere. Hence, storms, whether individual thunderstorms,extratropical rain or snow storms, or tropical cyclones, supplied with increased moisture, producemore intense precipitation events. Such events are observed to be widely occurring, even where totalprecipitation is decreasing: ‘it never rains but it pours!’ This increases the risk of flooding. The atmospheric and surface energy budget plays a critical role in the hydrological cycle, and also in theslower rate of change that occurs in total precipitation than total column water vapor. With modestchanges in winds, patterns of precipitation do not change much, but result in dry areas becomingdrier (generally throughout the subtropics) and wet areas becoming wetter, especially in the mid- tohigh latitudes: the ‘rich get richer and the poor get poorer’. This pattern is simulated by climate models and is projected to continue into the future. Because, with warming, more precipitation occurs asrain instead of snow and snow melts earlier, there is increased runoff and risk of flooding in earlyspring, but increased risk of drought in summer, especially over continental areas. However, withmore precipitation per unit of upward motion in the atmosphere, i.e. ‘more bang for the buck’, atmospheric circulation weakens, causing monsoons to falter. In the tropics and subtropics, precipitationpatterns are dominated by shifts as sea surface temperatures change, with El Niño a good example.The volcanic eruption of Mount Pinatubo in 1991 led to an unprecedented drop in land precipitationand runoff, and to widespread drought, as precipitation shifted from land to oceans and evaporationfaltered, providing lessons for possible geoengineering. Most models simulate precipitation that occursprematurely and too often, and with insufficient intensity, resulting in recycling that is too large anda lifetime of moisture in the atmosphere that is too short, which affects runoff and soil moisture.PP: jtmNational Center for Atmospheric Research, Box 3000, Boulder, Colorado 80307, USATS: bfKevin E. Trenberth*CE: smChanges in precipitation with climate changeC 953 3 Jan 2011Vol. doi: 10.3354/cr00953
Clim Res 2Precipitation (mm)40FloodingDroughtWild firesWilting plants20A: MonthlyAmount: 75 mmIntensity: 37.5 mm d–1Frequency: 6.7%040201611162126Soil moisture continually replenished;virtually no runoffB: MonthlyAmount: 75 mmIntensity: 3.75 mm d–1Frequency: 67%01611162126Fig. 1. Hypothetical daily amounts of precipitation for a monthat Stations A and B, including the monthly amounts, averageintensity per day conditional on rain occurring, and frequency.Consequences for runoff and plants are noted in each paneltremes in rainfall (from tropical storms, thunderstorms,orographic rainfall, widespread extratropical cyclones,etc.), while droughts are associated with a lack of precipitation and often extremely high temperatures thatcontribute to drying. Floods are often fairly local anddevelop on short time scales, while droughts are extensive and develop over months or years. Both can bemitigated; floods by good drainage systems and droughtby irrigation, for instance. Nonetheless, daily newspaper headlines of floods and droughts reflect thecritical importance of the water cycle, in particular precipitation, in human affairs. World flood damage estimates are in the billions of U.S. dollars annually, with1000s of lives lost; while drought costs are of similarmagnitude and often lead to devastating wildfires andheat waves. The loss of life and property from extremehydrological events has therefore caused society tofocus on the causes and predictability of these events.Tropical cyclones typically have the highest propertydamage loss of any extreme event, and are therefore ofgreat interest to state and local disaster preparednessorganizations, as well as to the insurance industry(Murnane 2004).Evidence is building that human-induced climatechange (global warming), is changing precipitationand the hydrological cycle, and especially the extremes. This article first discusses the observed changes(Section 2) and then considers the processes involvedand the conceptual basis for understanding changes inprecipitation, floods, and drought, and future prospects (Sections 3 and 4). Climate models (Section 5)have been used as a guide to future changes, butare challenged in their ability to correctly simulatepatterns, seasonal variations, and characteristics ofprecipitation, and hence their results must be usedwith caution (e.g. Kharin et al. 2007, Liepert & Previdi 2009). Outstanding issues are briefly discussed inSection 6.2. OBSERVED CHANGES IN PRECIPITATION2.1. Mean fieldsThere is a very strong relationship between total column water vapor (TCWV, also known as precipitablewater) and sea-surface temperatures (SSTs) over theoceans (Trenberth et al. 2005) in both the overallpatterns and their variations over time (e.g. Fig. 2 forJanuary and July). The Clausius-Clapeyron (C-C)equation describes the water-holding capacity of theatmosphere as a function of temperature, and typicalvalues are about 7% change for 1 C change in temperature. For SST changes, the TCWV varies with slightlylarger values owing to the increase in atmospherictemperature perturbations with height, especially inthe tropics. Accordingly, the largest average TCWVvalues occur over the tropical Pacific Warm Pool,where highest large-scale values of SSTs typicallyreside. The annual mean and January and July valuesare given in Table 1 for the global, ocean, and landdomains. Global surface air temperatures are higher inNorthern Hemisphere summers, and this is reflected inmuch higher TCWV values over land.The observed TCWV and precipitation mean annualcycles also show very strong relationships in the tropics and subtropics, but not in the extratropics (Fig. 2).Atmospheric convergence at low levels tends to occurin close association with the highest SSTs, although thefactors extend beyond the SST values alone to includethe gradients in SSTs, which are reflected in surfacepressure gradients and thus in the winds. Accordingly,in the tropics, the precipitation patterns tend to mimicthe patterns of TCWV and thus SSTs, but with muchmore structure and sharper edges, as overturning circulations, such as those associated with the HadleyCell and monsoons, develop and create strong areas ofsubsidence that dry out the troposphere above theboundary layer.The mean TCWV falls off at higher latitudes in bothhemispheres, along with the SSTs, but precipitationhas a secondary maximum over the oceans associatedwith mid-latitude storm tracks. In January these arestrongly evident over the North Pacific and AtlanticOceans and, to a lesser extent, throughout the southern oceans. The southern ocean storm tracks arestrongest in the transition seasons and broadest in thesouthern winter, while the northern ocean storm tracksbecome weaker in the northern summer. The absenceof relationships between mean TCWV and precipitation in the extratropics highlights the very transientnature of precipitation events that are associated withextratropical cyclones, while in the tropics there is amuch stronger mean-flow component associated withmonsoons and the Hadley circulation.
Trenberth: Changes in precipitation with climate change3Fig. 2. Mean sea-surface temperature (SST), total column water vapour (TCWV), and precipitation for January (left panels) andJuly (right panels). SSTs are from Smith et al. (2008) for 1979–2008; TCWV is from SSM/I over ocean and National Centers forEnvironmental Prediction reanalyses over land (see Trenberth et al. 2007b) for 1987–2008; and precipitation is from the GlobalPrecipitation Climatology Project Ver. 2.1 for 1979–2008 based on Huffman et al. (2009). Graphs to the right: zonal means; values,top right: global meanDifficulties in the measurement of precipitationremain an area of concern in quantifying the extent towhich global and regional scale precipitation haschanged. In situ measurements are especially impacted by wind effects on the gauge catch, especiallyfor snow and light rain (Adam & Lettenmaier 2003),and few measurements exist in areas of steep and complex topography (Adam et al. 2006). For remotelysensed measurements (radar and space-based), thegreatest problems are that only measurements of instantaneous rates can be made and there are uncertainties in algorithms for converting radiometric measurements (radar, microwave, infrared) into precipitation rates at the surface (e.g. Krajewski et al. 2010). Togain confidence in observations, it is useful to examinethe consistency of changes in a variety of complementary moisture variables, including both remotelysensed and gauge-measured precipitation, drought,evaporation, atmospheric moisture, soil moisture, andstream flow, although uncertainties exist with all ofthese variables as well (Huntington 2006).2.2. Changes in water vaporAs the climate warms, water-holding capacity increases with higher temperatures according to the C-Crelationship, and, hence, it is natural to expect increases in water vapor amounts because relative humidity is more likely to remain about the same. Changes
4Clim Res satellites. Gu et al. (2007) documentedglobal and tropical rainfall changesusing the Global Precipitation ClimaSST ( C)TCWV (mm)Precipitation (mm d–1)tology Project (GPCP), and found nearAnnual Jan Jul Annual Jan JulAnnual Jan Julzero global changes, but with largevariability and changes over land thatGlobal ocean 18.2 18.2 18.3are largely compensated for by oppoGlobal24.2 23.1 25.82.672.69 2.70Ocean26.6 26.3 27.02.872.92 2.79site changes over the oceans. This isLand18.5 15.5 23.02.212.16 2.50especially the case for El Niño events(Trenberth & Dai 2007). The globalmean GPCP precipitation is 2.67 mm d–1, correspondin TCWV and humidity are evident in observations.At the surface, there are clear indications of increasesing to 76 W m–2 in terms of latent heating. An update ofin specific humidity (Dai 2006a, Willett et al. 2008).the Gu et al. analysis (also Huffman et al. 2009) conOver oceans, the increases are consistent with C-Cfirms that there have been no significant trends sinceexpectations, with a constant relative humidity, while1979 (Fig. 3). This is in marked contrast to the results ofincreases are somewhat lower over land, especiallyWentz et al. (2007), who found a significant upwardwhere water availability is limited. In the tropospheretrend from 1987 to 2006, but their results depend critithe largest fluctuations in TCWV occur with El Niño–cally on the time period and also the dataset used.Southern Oscillation (ENSO) events (Trenberth et al.Fig. 3 also reveals an upward trend over the period2005), although a sharp drop was evident following theobserved by Wentz, but it is not robust as it does notMount Pinatubo eruption (Durre et al. 2009). TCWVstand up to addition of data at either end.has also increased at rates consistent with C-C for theNew observations suggest that the GPCP values mayperiod 1987–2004 (1.3% decade–1) (Trenberth et al.be an underestimate, because they may not ade2005, 2007a), and the relationship with changes inquately capture low-level warm rain in the extratropSSTs is sufficiently strong that it is possible to deduceics, and the high extremes could be underestimated asan increase of about 4% in TCWV over the oceanswell. Trenberth et al. (2007b, 2009) assessed the evisince the 1970s. Over land in the Northern Hemidence and increased the GPCP estimate by 5% oversphere, Durre et al. (2009) found trends indicating anthe ocean to better satisfy energy budget constraints,increase of 0.45 mm decade–1 (1973–2006) in TCWV,so that the latent heat released by precipitation wasbut homogeneity issues remain in the radiosondeassigned a value of 80 W m–2. The main variations inrecords. Water vapor in the upper troposphere has alsothe global mean precipitation occur in the tropicsincreased at a rate consistent with a fairly constant rel(Fig. 3), where TCWV is largest, in association withative humidity (Soden et al. 2005). Santer et al. (2007)ENSO events. However, even though the regionalhave identified a strong human influence in the recentvariations of precipitation with ENSO are huge (cf.water vapor increases.Trenberth & Caron 2000), the zonal and global meansThe observed increases in water vapor affect bothare much more muted, owing to cancellation betweenthe greenhouse effect, thus providing a positive feeddipole structures, although ENSO accounts for theback to climate change, and the hydrological cycle, bymain land –sea variations (Gu et al. 2007).providing more atmospheric moisture for all stormsOver land, the precipitation record extends throughto feed upon. Accordingly, it has ramifications for preout the 20th century, and large variations occur fromcipitation.year to year and on decadal time scales. Nonetheless,some large-scale patterns of systematic change areevident (Trenberth et al. 2007a). In general, there have2.3. Changes in precipitationbeen decreases in precipitation in the subtropics andtropics outside of the monsoon trough, and increasesA comprehensive summary of observed changes inin land precipitation at higher latitudes, notably overprecipitation is given in the Intergovernmental PanelNorth America, Eurasia, and Argentina. The decreaseson Climate Change (IPCC) Fourth Assessment (AR4)are especially evident in the Mediterranean, southern(Trenberth et al. 2007a), and the reader is referredAsia, and throughout Africa. In the more northernthere for the extensive bibliography. Schlosser & Houserregions, more precipitation falls as rain rather than(2007) and Wentz et al. (2007) provided recent estisnow (e.g. Mote 2003, Knowles et al. 2006). The liquidmates of precipitation and their trends. However, theprecipitation season has become longer by up to 3 wkprecipitation and evaporation estimates of Schlosserin some regions of the boreal high latitudes over the& Houser (2007) are out of balance and reveal likelylast 50 yr (Trenberth et al. 2007a), owing, in particular,spurious changes over time associated with changes into an earlier onset of spring. Similar changes can beTable 1. Global, ocean, and land means for annual, January, and July seasurface temperature (SST), total column water vapor (TCWV), and precipitation
Trenberth: Changes in precipitation with climate change5Fig. 3. Time series of precipitation from the Global Precipitation Climatology Project relative to their 1979–2008 mean of 2.67 mmd–1 globally (top panel). Global values are dominated by variations in the tropics. Zonally integrated values are given in the other3 panels for 30 N–30 S for total, ocean, and land precipitation (panels labeled accordingly). Standard deviations are given atright. Land values are typically a factor of 5 lower than those for ocean. The dominant variations are associated with ElNiño–Southern Oscillation, but large cancellation occurs both in longitude and latitude. The values are smoothed with a 13-termfilter to remove fluctuations of less than about a yearinferred over the oceans from the large-scale patternsof change in salinity from the 1950s–1960s versusthe 1990s–2000s (IPCC 2007). Higher salinities of theoceans at low latitudes and freshening at high latitudesof both hemispheres are evident.Another perspective on total land precipitationcomes from examining precipitation in conjunctionwith river discharge into the oceans (Dai et al. 2009) forthe period 1948–2005 (see Fig. 4). This reinforces theother analyses mentioned above. The results alterconclusions published earlier (Gedney et al. 2006), asthere is large sensitivity to how missing data aretreated. At interannual to decadal time scales, resultsrevealed large variations in continental discharge correlated with ENSO for the discharge into the Pacific,Atlantic, Indian, and global oceans as a whole (but notwith discharges into the Arctic Ocean and the Mediter-ranean and Black Seas). For most ocean basins and theglobal oceans as a whole, the discharge data showdownward trends, and precipitation changes are foundto be the main cause. For the Arctic drainage areas,upward trends in streamflow from 1948 to 2005 wereapparently not accompanied by increasing precipitation (although the data may not be adequate), especially over the Siberia, and decreasing trends in snowcover and soil ice water content over the northernhigh-latitudes may have contributed to the runoffincreases in these regions.The global land values of precipitation after 1950(Fig. 5) (Trenberth & Dai 2007) show a slight decreaseoverall for this time period, but with a singular drop in1992 in both streamflow and precipitation that is welloutside the realm of all other variations and is associated with the Mount Pinatubo eruption in 1991 (Tren-
6Clim Res Fig. 4. Linear trends in river discharge as linked to the associated drainage basin (adapted from Dai et al. 2009)2002, Klein Tank & Können 2003, Groisman et al. 2004,berth & Dai 2007). The abrupt drop in incoming net2005, Alexander et al. 2006, Klein Tank et al. 2006,radiation from the sun led to a brief cooling of the landTrenberth et al. 2007a, Groisman & Knight 2008).and then the ocean, which initially caused a shift inMuch of this increase occurred during the last 3precipitation away from the land and then decreaseddecades of the century. Although flooding has inthe global evaporation, TCWV (Durre et al. 2009), andcreased in some areas, and in association with tropiglobal precipitation.cal cyclones and hurricanes, land-use change altersDrought has also generally increased throughout therisk, and flood mitigation projects are pervasive in20th century (Dai et al. 2004, Trenberth et al. 2007a), asreducing flood risks. Nevertheless, extreme floodingmeasured by the Palmer drought severity index (PDSI).has increased in the 20th century (Milly et al. 2002).Dai et al. (2004) show that very dry land areas acrossKarl & Trenberth (2003) and Alla
nature of precipitation events that are associated with extratropical cyclones, while in the tropics there is a much stronger mean-flow component associated with monsoons and the Hadley circulation. 40 20 0 40 20 0 Precipitation (mm) 1 6 11 16 21 26 1 6 11 16 21 26 Drought Wild fires Flooding Wilting plants Soil moisture continually replenished;
Oct 14, 2021 · Atmosphere 2021, 12, 1346 4 of 12 where x denotes the original model precipitation; y denotes the calibrated precipitation; OBSk is the precipitation grading that selects five grades, namely, 0.1, 2, 4, 8, and 20; and xk is the new precipitation grading. For the FM method, xk is the model threshold with the same frequency as that of the observed OBSk.
Visualizing Climate / Climate Variability and Short-Term Forecasting VISUALIZING CLIMATE . To describe how climate has traditionally been held to be the synthesis of weather conditions, both the average of parameters, generally temperature and precipitation, over a period of time and
A. General Physiography and Climate of Tamil Nadu 0 B. TNICP Project Locations 1 IV. Climate, Observed Trends and Climate Change in Tamil Nadu 3 A. The Baseline Climate 3 B. Observed Climate Trends 4 1. Temperature Trends - Tamil Nadu State 4 2. Rainfall Trends 5 3. Temperature and Precipitation Extremes Recorded in Tamil Nadu 5
to diminish and summer wa-ter supply will likely decline. Precipitation varies both spa-tially, or, across the land-scape, and temporally (through time). Mountain ranges play an important role in where precipitation falls in the PNW. The highest annual precipitation amounts are found on the windward, or, Water and Climate in the Pacific Northwest
Nov 12, 2020 · Soil Climate Analysis Network (SCAN) This chart shows the precipitation and soil moisture for the last 30 days at the . Vernon SCAN site in Texas. Precipitation between October 25-29 increased soil moisture at the -2”, -4”, -8”, and -20” sensors. Accumulated precipitation for the
Extreme precipitation refers to an episode of abnormally high rainfall. The word “extreme” may vary depending on location, season, and length of historical record. These events are defined as days with precipitation in the top one percent of days with precipitation (U.S. Global Change, 2019).
Step 6. Calculate the mean storm event precipitation depth at the project site, called (P 6) site. Multiply the mean storm event precipitation depth for the rain gage chosen by a correction factor, which is the ratio of the mean annual precipitation at the site (MAP site) to the mean annual precipitation at the rain gage (MAPgage).
Michigan. Lake effects cause 25 to 100 percent greater snowfall along the eastern shore. Average lake precipitation is 4 percent higher in winter, 7 percent lower in spring, and 14 percent lower in summer than basin land precipitation; they are equal in fall. Reference: Changnon, Stanley A., Jr Precipitation Climatology of Lake Michigan Basin.
