Seasonal and Interannual Variability of Wet and Dry Spells over Two Urban Regions in the Western Maritime Continent

Abstract Daily rainfall data from two urban regions in Southeast Asia are analyzed to study seasonal and interannual variability of wet and dry spells. The analysis is carried out using 35 years of data from Singapore and 23 years of data from Jakarta. The frequency distribution of wet (dry) spells and their relative contribution to the total number of wet (dry) days and to the total rainfall are studied using 15 statistical indicators. At the annual scale, Singapore has a greater number of wet spells and a larger mean wet spell length compared to Jakarta. However, both cities have equal probability of extreme wet spells. Seasonal-scale analysis shows that Singapore is drier (wetter) than Jakarta during boreal winter (summer). The probability of extreme wet spells is lower (higher) for Singapore than Jakarta during boreal winter (summer). The results show a stronger contrast between Singapore and Jakarta during boreal summer. The study also examined the time series of Singapore wet and dry spell indicators for the presence of interannual trends. The results indicate statistically significant upward trends for a majority of wet spell indicators. The wet day percentage and mean wet spell length are increasing at 2.0% decade−1 and 0.18 days decade−1, respectively. Analysis of dynamic and thermodynamic variables from ERA-Interim during the study period indicates a strengthening of low-level convergence and vertical motion and an increase in specific humidity and atmospheric instability (convective available potential energy), which explain the increasing trends observed in Singapore wet spell indicators.

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Spatial and Temporal Analysis of Dry and Wet Spells in Upper Awash River Basin, Ethiopia

Water ◽

10.3390/w12113051 ◽

2020 ◽

Vol 12 (11) ◽

pp. 3051

Author(s):

Girma Berhe Adane ◽

Birtukan Abebe Hirpa ◽

Chul-Hee Lim ◽

Woo-Kyun Lee

Keyword(s):

River Basin ◽

Management Practices ◽

Markov Chain Model ◽

Temporal Analysis ◽

Chain Model ◽

Rainfall Analysis ◽

Dry Spells ◽

Dry Spell ◽

Awash River Basin ◽

Wet Spells

This study aimed to analyze the probability of the occurrence of dry/wet spell rainfall using the Markov chain model in the Upper Awash River Basin, Ethiopia. The rainfall analysis was conducted in the short rainy (Belg) and long rainy (Kiremt) seasons on a dekadal (10–day) scale over a 30-year period. In the Belg season, continuous, three-dekad dry spells were prevalent at all stations. Persistent dry spells might result in meteorological, hydrological, and socio-economic drought (in that order) and merge with the Kiremt season. The consecutive wet dekads of the Kiremt season indicate a higher probability of wet dekads at all stations, except Metehara. This station experienced a short duration (dekads 20–23) of wet spells, in which precipitation is more than 50% likely. Nevertheless, surplus rainwater may be recorded at Debrezeit and Wonji only in the Kiremt season because of a higher probability of wet spells in most dekads (dekads 19–24). At these stations, rainfall can be harvested for better water management practices to supply irrigation during the dry season, to conserve moisture, and to reduce erosion. This reduces the vulnerability of the farmers around the river basin, particularly in areas where dry spell dekads are dominant.

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Dynamics of Interannual Variability in Summer Precipitation over East Asia*

Journal of Climate ◽

10.1175/2011jcli4099.1 ◽

2011 ◽

Vol 24 (20) ◽

pp. 5435-5453 ◽

Cited By ~ 80

Author(s):

Yu Kosaka ◽

Shang-Ping Xie ◽

Hisashi Nakamura

Keyword(s):

East Asia ◽

Interannual Variability ◽

Southern Oscillation ◽

Wave Train ◽

Polar Front ◽

Boreal Summer ◽

Boreal Winter ◽

Temperature Advection ◽

Svd Analysis ◽

Precipitation Anomalies

Abstract The summertime mei-yu–baiu rainband over East Asia displays considerable interannual variability. A singular value decomposition (SVD) analysis for interannual variability reveals that precipitation anomalies over the mei-yu–baiu region are accompanied by in situ anomalies of midtropospheric horizontal temperature advection. Anomalous warm (cool) advection causes increased (decreased) mei-yu–baiu precipitation locally by inducing adiabatic ascent (descent). The anomalous precipitation acts to reinforce the vertical motion, forming a feedback system. By this mechanism, the remotely forced anomalous atmospheric circulation can induce changes in mei-yu–baiu precipitation. The quasi-stationary precipitation anomalies induced by this mechanism are partially offset by transient eddies. The SVD analysis also reveals the association of mei-yu–baiu precipitation anomalies with several teleconnection patterns, suggesting remote induction mechanisms. The Pacific–Japan (PJ) teleconnection pattern, which is associated with anomalous convection over the tropical western North Pacific, contributes to mei-yu–baiu precipitation variability throughout the boreal summer. The PJ pattern mediates influences of the El Niño–Southern Oscillation in preceding boreal winter on mei-yu–baiu precipitation. In early summer, the leading covariability pattern between precipitation and temperature advection also features the Silk Road pattern—a wave train along the summertime Asian jet—and another wave train pattern to the north along the polar-front jet that often leads to the development of the surface Okhotsk high.

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Water Vapor Fluxes over the Intra-Americas Sea: Seasonal and Interannual Variability and Associations with Rainfall

Journal of Climate ◽

10.1175/jcli4096.1 ◽

2007 ◽

Vol 20 (9) ◽

pp. 1910-1922 ◽

Cited By ~ 66

Author(s):

Alberto M. Mestas-Nuñez ◽

David B. Enfield ◽

Chidong Zhang

Keyword(s):

United States ◽

Gulf Of Mexico ◽

Interannual Variability ◽

Boreal Summer ◽

Boreal Winter ◽

The North ◽

The Pacific ◽

Central United States ◽

Low Level Jet ◽

The Caribbean

Abstract The seasonal and interannual variability of moisture transports over the Intra-Americas Sea (including the Gulf of Mexico and the Caribbean Sea) is evaluated using the NCEP–NCAR global reanalysis. The seasonal variability of these moisture transports is consistent with previous studies and shows distinctive winter and summer regimes. Boreal winter moisture is mainly delivered to the central United States from the Pacific with some contribution from the Gulf of Mexico. It is during the boreal summer that the moisture flow over the Intra-Americas Sea is most effective in supplying the water vapor to the central United States via the northern branch of the Caribbean low-level jet. The increase of intensity of this jet during July is associated with an increase in evaporation over the Intra-Americas Sea, consistent with midsummer drought conditions over this region. During both summer and winter, the interannual variability of the inflow of moisture from the Intra-Americas Sea into central United States is associated with Caribbean low-level jet variability. The source of the varying moisture is mainly the Gulf of Mexico and the North Atlantic area just east of the Bahamas Islands and the sink is precipitation over east-central United States. The main teleconnection pattern for these interannual variations appears to be the Pacific–North American, although in boreal winter ENSO and possibly the North Atlantic Oscillation may also play a role. During boreal summer, associations with ENSO mainly involve the zonal moisture exchange between the Intra-Americas Sea/tropical Atlantic and the tropical Pacific.

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Future Changes in Wet and Dry Season Characteristics in CMIP5 and CMIP6 simulations

Journal of Hydrometeorology ◽

10.1175/jhm-d-21-0017.1 ◽

2021 ◽

Author(s):

Caroline M. Wainwright ◽

Emily Black ◽

Richard P. Allan

Keyword(s):

Climate Change ◽

South America ◽

West Africa ◽

Southern Africa ◽

Dry Season ◽

Maximum Temperature ◽

Wet Season ◽

Dry Spells ◽

Dry Spell ◽

Spell Length

AbstractClimate change will result in more dry days and longer dry spells, however, the resulting impacts on crop growth depend on the timing of these longer dry spells in the annual cycle. Using an ensemble of Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6) simulations, and a range of emission scenarios, here we examine changes in wet and dry spell characteristics under future climate change across the extended tropics in wet and dry seasons separately. Delays in the wet seasons by up to two weeks are projected by 2070-2099 across South America, Southern Africa, West Africa and the Sahel. An increase in both mean and maximum dry spell length during the dry season is found across Central and South America, Southern Africa and Australia, with a reduction in dry season rainfall also found in these regions. Mean dry season dry spell lengths increase by 5-10 days over north-east South America and south-west Africa. However, changes in dry spell length during the wet season are much smaller across the tropics with limited model consensus. Mean dry season maximum temperature increases are found to be up to 3°C higher than mean wet season maximum temperature increases over South America, Southern Africa and parts of Asia. Longer dry spells, fewer wet days, and higher temperatures during the dry season may lead to increasing dry season aridity, and have detrimental consequences for perennial crops.

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Wet and dry spells in Senegal: comparison of detection based on satellite products, reanalysis, and in situ estimates

Natural Hazards and Earth System Science ◽

10.5194/nhess-21-1051-2021 ◽

2021 ◽

Vol 21 (3) ◽

pp. 1051-1069

Author(s):

Cheikh Modou Noreyni Fall ◽

Christophe Lavaysse ◽

Mamadou Simina Drame ◽

Geremy Panthou ◽

Amadou Thierno Gaye

Keyword(s):

Measurement Techniques ◽

West African Monsoon ◽

Tropical Rainfall Measuring Mission ◽

Early Warning Systems ◽

Rain Gauge ◽

Major Influence ◽

Dry Spells ◽

Dry Spell ◽

Spatio Temporal ◽

Wet Spells

Abstract. In this study, the detection and characteristics of dry/wet spells (defined as episodes when precipitation is abnormally low or high compared to usual climatology) drawn from several datasets are compared for Senegal. Here, four datasets are based on satellite data (TRMM-3B42 V7, CMORPH V1.0, TAMSAT V3, and CHIRPS V2. 0), two on reanalysis products (NCEP-CFSR and ERA5), and three on rain gauge observations (CPC Unified V1.0/RT and a 65-rain-gauge network regridded by using two kriging methods, namely ordinary kriging, OK, and block kriging, BK). All datasets were converted to the same spatio-temporal resolution: daily cumulative rainfall on a regular 0.25∘ grid. The BK dataset was used as a reference. Despite strong agreement between the datasets on the spatial variability in cumulative seasonal rainfall (correlations ranging from 0.94 to 0.99), there were significant disparities in dry/wet spells. The occurrence of dry spells is less in products using infrared measurement techniques than in products coupling infrared and microwave, pointing to more frequent dry spell events. All datasets show that dry spells appear to be more frequent at the start and end of rainy seasons. Thus, dry spell occurrences have a major influence on the duration of the rainy season, in particular through the “false onset” or “early cessation” of seasons. The amplitude of wet spells shows the greatest variation between datasets. Indeed, these major wet spells appear more intense in the OK and Tropical Rainfall Measuring Mission (TRMM) datasets than in the others. Lastly, the products indicate a similar wet spell frequency occurring at the height of the West African monsoon. Our findings provide guidance in choosing the most suitable datasets for implementing early warning systems (EWSs) using a multi-risk approach and integrating effective dry/wet spell indicators for monitoring and detecting extreme events.

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Reinitiation of the Boreal Summer Intraseasonal Oscillation in the Tropical Indian Ocean*

Journal of Climate ◽

10.1175/jcli3516.1 ◽

2005 ◽

Vol 18 (18) ◽

pp. 3777-3795 ◽

Cited By ~ 75

Author(s):

Xian-An Jiang ◽

Tim Li

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Intraseasonal Oscillation ◽

Circulation Model ◽

Equatorial Indian Ocean ◽

Specific Humidity ◽

Boreal Summer ◽

Boreal Winter ◽

Boreal Summer Intraseasonal Oscillation ◽

Temperature Advection

Abstract The characteristic features of the boreal summer intraseasonal oscillation (BSISO) during its reinitiation period are studied using NCEP–NCAR reanalysis. Based on these observations and with the aid of an anomalous atmospheric general circulation model (AGCM), a possible mechanism responsible for the BSISO reinitiation is elucidated. The western equatorial Indian Ocean along the eastern African coast tends to be a key region for the phase transition of the BSISO from an enhanced to suppressed convective phase, or vise versa. The major precursory feature associated with reinitiation of suppressed convection is found in the divergence and reduced specific humidity in the boundary layer. Numerical experiments indicate that the low-level divergence is caused by the cold horizontal temperature advection and associated adiabatic warming (descending motion) in situ. The summer mean state is found to be important for the cold horizontal temperature advection through the modulation of a Gill-type response to an intraseasonal oscillation (ISO) heating in the eastern equatorial Indian Ocean. The results in this study suggest a self-sustained paradigm in the Indian Ocean for the BSISO; that is, the BSISO could be a basinwide phenomenon instead of a global circumstance system as hypothesized for the boreal winter ISO (i.e., the Madden–Julian oscillation).

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Droughts and the Impacts of Dry Spells in North of Iraq

Research in Ecology ◽

10.30564/re.v3i1.2865 ◽

2021 ◽

Vol 3 (1) ◽

Author(s):

Safieh Javadinejad ◽

David Hannah ◽

Stefan Krause ◽

Rebwar Dara ◽

Forough Jafary ◽

...

Keyword(s):

Temporal Analysis ◽

Distribution Functions ◽

Spi Index ◽

The North ◽

Generalized Pareto ◽

Dry Spells ◽

Dry Spell ◽

Complete Series ◽

Drought Occurrence ◽

Spell Length

Different sets of dry spell length such as complete series, monthly maximum, seasonal maximum, and annual maximum are applied and modeled with different probability distribution functions (such as Gumbel Max, generalized extreme value, Log-Logistic, generalized logistic, inverse Gaussian, Log-Pearson 3, generalized Pareto) to recognize in which duration, dry spells cause drought. The drought situation and temporal analysis in the North of Iraq region were done using the SPI index and by software of DrinC at a time scale of 3.6 and 12 months. Because of applicability, availability of data and the aim of the study, SPI is selected to analyze the dry spells in this study. Based on the maximum length of the available statistical period, the statistics for the years 1980 to 2019 were used from nine meteorological stations for analysis. The results of the study showed the severity of drought during the study period which related to dry spells. The results of this research confirm the variation of drought occurrence with varying degrees in different time and different dry spells condition in Iraq.

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Observed Increase of TTL Temperature and Water Vapor in Polluted Clouds over Asia

Journal of Climate ◽

10.1175/2010jcli3749.1 ◽

2011 ◽

Vol 24 (11) ◽

pp. 2728-2736 ◽

Cited By ~ 26

Author(s):

Hui Su ◽

Jonathan H. Jiang ◽

Xiaohong Liu ◽

Joyce E. Penner ◽

William G. Read ◽

...

Keyword(s):

Water Vapor ◽

Radiative Heating ◽

Specific Humidity ◽

Boreal Summer ◽

Boreal Winter ◽

Maritime Continent ◽

Ice Clouds ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Higher Temperature

Abstract Satellite observations are analyzed to examine the correlations between aerosols and the tropical tropopause layer (TTL) temperature and water vapor. This study focuses on two regions, both of which are important pathways for the mass transport from the troposphere to the stratosphere and over which Asian pollution prevails: South and East Asia during boreal summer and the Maritime Continent during boreal winter. Using the upper-tropospheric carbon monoxide measurements from the Aura Microwave Limb Sounder as a proxy of aerosols to classify ice clouds as polluted or clean, the authors find that polluted clouds have a smaller ice effective radius and a higher temperature and specific humidity near the tropopause than clean clouds. The increase in water vapor appears to be related to the increase in temperature, as a result of increased aerosols. Meteorological differences between the clouds cannot explain the differences in temperature and water vapor for the polluted and clean clouds. The authors hypothesize that aerosol semidirect radiative heating and/or changes in cirrus radiative heating, resulting from aerosol microphysical effects on clouds, may contribute to the increased TTL temperature and thus increased water vapor in the polluted clouds.

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