EVALUASI PERFORMA INDEKS MONSUN AUSMI DAN WNPMI DI WILAYAH INDONESIA

Intisari Iklim di wilayah Indonesia sangat dipengaruhi oleh aktivitas monsun Asia-Australia. Variabilitas kedua sistem monsun tersebut dapat direpresentasikan dengan baik masing-masing oleh indeks monsun Australian Summer Monsoon Index (AUSMI) dan Western North Pacific Monsoon Index (WNPMI). Saat ini, BMKG secara operasional menggunakan indeks AUSMI dan WNPMI untuk memonitor aktivitas monsun di wilayah Indonesia sebagai bahan prakiraan musim. Meskipun banyak literatur menyatakan bahwa wilayah Indonesia merupakan bagian dari sistem monsun Asia-Australia, namun kondisi topografi lokal yang kompleks berpotensi memodifikasi sirkulasi monsun sehingga perlu dikaji performa kedua indeks tersebut sebelum digunakan secara operasional. Penelitian ini dilakukan untuk menguji performa indeks monsun AUSMI dan WNPMI dalam menggambarkan variasi antartahunan (interannual), variasi dalam musim (intraseasonal), dan siklus tahunan (annual cycle) hujan monsun Indonesia. Hasil penelitian mengungkapkan bahwa kedua indeks memiliki performa yang sangat baik hanya di wilayah dimana indeks tersebut didefinisikan namun kurang baik untuk wilayah Indonesia seperti yang ditunjukan oleh nilai koefisien korelasi yang tidak signifikan dari hasil uji statistik antara kedua indeks dengan curah hujan dari Global Precipitation Climatology Project (GPCP) pada periode 1981-2010. Selain itu, kedua indeks juga memperlihatkan karakteristik siklus tahunan yang berbeda dengan karakteristik siklus tahunan hujan wilayah Jawa sebagai wilayah kunci monsun Indonesia. Hasil ini mengindikasikan perlunya pendefinisian indeks sendiri untuk memonitor aktivitas monsun di wilayah Indonesia. Abstract The climate of Indonesia is strongly affected by the Asian-Australian monsoon system. The variability of the two monsoon systems can be well represented by the Western North Pacific Monsoon Index (WNPMI) and the Australian Summer Monsoon Index (AUSMI) respectively. For producing seasonal forecast, BMKG uses the WNPMI and AUSMI monsoon index to monitor monsoon activity in Indonesia. Although most literature states that the Indonesian region is part of the Asian-Australian monsoon system, the complex local topography may modify the monsoon circulation. Hence, it is necessary to assess the performance of the two indices before they are operationally used. This study was conducted to evaluate the performance of the AUSMI and WNPMI monsoon indices in describing the annual cycle, intraseasonal and interannual variability of the Indonesian monsoon rainfall. The results revealed that the two indices only performed very well in the areas where the index was defined but lack of skill for the Indonesian region because of insignificant linear correlation based on a statistical significance test between the two indices and the Global Precipitation Climatology Project (GPCP) rainfall in the 1981-2010 period. In addition, both monsoon indices and Java rainfall showed different characteristics of the annual cycle. These results indicate that it is necessary to define a specific index for monitoring monsoon activity in Indonesia.

Rainfall in Vietnam

<p>The thesis is a comprehensive analysis of the climate of Vietnam, concentrating on rainfall. Vietnam lies in the tropical northern hemisphere in a region that is influenced by the South Asian, East Asian and Australian monsoons. Rainfall here is associated with several different mechanisms, such as the monsoon, tropical cyclones, topography, and so on. From the initial climatological analysis, monsoon and non-monsoon rainfall is investigated. Non-monsoon rainfall is found to be related to a vortex often found off the coast of Vietnam, a newly-understood extension of the “Borneo vortex”. The thesis begins with a study of the surface climate and the general atmospheric circulation over the Southeast Asian region, which dominates Vietnam’s climate. Trends of surface temperature and rainfall were investigated for a 40 year period (1971-2010), using a newly-extended dataset of 60 stations. Vietnam’s average temperature has increased at a rate of 0.26 ± 0.10°C per decade since the 1970s, approximately twice the rate of global warming over the same period. The increase in temperature is statistically significant in most sub-regions. Trends in rainfall are however mostly insignificant in that period. Temperature and rainfall variability are shown to be linked to ENSO on both a national and sub-regional scale. The rainfall climate of Vietnam has been studied in depth, particularly the characteristics of monsoon rainfall and the variability of the length of wet and dry seasons. That investigation has led to the development of an objective monsoon index, based on regional mean sea level pressure and low level zonal wind. While originally developed to define onset and withdrawal dates for the monsoon in Vietnam and over Southeast Asia, the index is shown to be applicable in all monsoon regions of the globe, the first objective index to have such global utility. The final part of the thesis deals with tropical vortex activity and its associated rainfall. Vortices exist almost year-round, migrating from the coast of Vietnam – Southeast Asian Sea - Philippines in summer to the Borneo Island region in winter. Clear evidence is found for the presence of a semi-permanent vortex near the south coast of Vietnam or the north of the Southeast Asian Sea – Maritime Continent (SEASMC) region. It is this vortex and the tropical cyclones over the SEASMC region that significantly contribute to the Vietnam rainfall, particularly the post-monsoon rainfall in Central Vietnam.</p>

Rainfall in Vietnam

<p>The thesis is a comprehensive analysis of the climate of Vietnam, concentrating on rainfall. Vietnam lies in the tropical northern hemisphere in a region that is influenced by the South Asian, East Asian and Australian monsoons. Rainfall here is associated with several different mechanisms, such as the monsoon, tropical cyclones, topography, and so on. From the initial climatological analysis, monsoon and non-monsoon rainfall is investigated. Non-monsoon rainfall is found to be related to a vortex often found off the coast of Vietnam, a newly-understood extension of the “Borneo vortex”. The thesis begins with a study of the surface climate and the general atmospheric circulation over the Southeast Asian region, which dominates Vietnam’s climate. Trends of surface temperature and rainfall were investigated for a 40 year period (1971-2010), using a newly-extended dataset of 60 stations. Vietnam’s average temperature has increased at a rate of 0.26 ± 0.10°C per decade since the 1970s, approximately twice the rate of global warming over the same period. The increase in temperature is statistically significant in most sub-regions. Trends in rainfall are however mostly insignificant in that period. Temperature and rainfall variability are shown to be linked to ENSO on both a national and sub-regional scale. The rainfall climate of Vietnam has been studied in depth, particularly the characteristics of monsoon rainfall and the variability of the length of wet and dry seasons. That investigation has led to the development of an objective monsoon index, based on regional mean sea level pressure and low level zonal wind. While originally developed to define onset and withdrawal dates for the monsoon in Vietnam and over Southeast Asia, the index is shown to be applicable in all monsoon regions of the globe, the first objective index to have such global utility. The final part of the thesis deals with tropical vortex activity and its associated rainfall. Vortices exist almost year-round, migrating from the coast of Vietnam – Southeast Asian Sea - Philippines in summer to the Borneo Island region in winter. Clear evidence is found for the presence of a semi-permanent vortex near the south coast of Vietnam or the north of the Southeast Asian Sea – Maritime Continent (SEASMC) region. It is this vortex and the tropical cyclones over the SEASMC region that significantly contribute to the Vietnam rainfall, particularly the post-monsoon rainfall in Central Vietnam.</p>

Analysis of climate indicator association with hotspots in Indonesia using heterogeneous correlation map

In several regions, land and forest fires of Indonesia occurred almost annually during the drought season. The severity of Indonesia's drought season is mainly influenced by the Australian Monsoon, local cloud formation controlled by Sea Surface Temperature (SST) around Indonesia. Moreover, it affects the severity of land and forest fires itself indirectly. This research aims to examine the association of the Australian Monsoon and local SST with land and forest fires in Indonesia. This research uses the Australian Monsoon Index (AUSMI) as an indicator for the Australian Monsoon and SST in the Karimata Strait and the Java Sea as indicators of local SST. An indicator of land and forest fires that will be used is the number of hotspots. A heterogeneous Correlation Map (HCM) is used to describe hotspots associated with AUSMI and local SST. The analysis shows that the east wind pattern of AUSMI associated with hotspots in Indonesia, especially in years when zonal winds enter an upward phase more slowly. Karimata Strait’s SST is associate with hotspots in the coastal part of Riau. Meanwhile, Java Sea’s SST is associate with hotspots in Lampung, South Sumatra, Jambi, and Kalimantan.

Analysis of Characteristics of Hydrological and Meteorological Drought Evolution in Southwest China

Based on the data of 82 meteorological stations and six representative hydrological stations in four provinces in Southwest China (Guizhou, Sichuan, Yunnan, Chongqing), this paper uses standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI) to analyze the spatial and temporal evolution characteristics of drought in the study area from 1968 to 2018. Combined with the Southwest monsoon index and historical drought data, the correlation of drought and the applicability of different drought indices were verified. The results show that: (1) SPEI-12 in Southwest China shows a downward trend from 1968 to 2018, with a linear trend rate of −0.074/10a, and SPEI-3 has a downward trend in four seasons, the maximum linear trend rate being −0.106/10a in autumn;(2) The change in SRI-12 and SRI-24 value directly reflected the decrease in SRI value, indicating that drought events are increasing in recent times, especially in the 21st century (3). Severe drought occurred in the south of Southwest China, as indicated by the increase of drought frequency in this area. The main reason for the variations in the frequency distribution of drought in Southwest China is the combined effect of the change of precipitation and evapotranspiration. (4) The correlation between hydrological drought index and disaster areas is stronger than the correlation between meteorological drought and disaster areas.

Ramification of Global and Local Climatic Variability on Resurgent Cases of Dengue in Delhi, India

It has become evident that the global climate is changing rapidly over the past few decades. The variation and change in the global climatic factors have a notable impact on the local climate of a region. The changing climate is widely regarded as one of the most serious global health threats of the 21st century. Among various kinds of diseases, the most vulnerable to these changes are vector-borne diseases. In the Indian context, particularly Delhi city is the most vulnerable to dengue, a kind of vector-borne disease having its highest impact. We sought to identify and explore the correlation and influence of the global climatic phenomena and local climatic factors with the reported number of dengue cases in Delhi. The temporal expansions of reported dengue cases in Delhi have a variation from its first major outbreak in the city during the year 1996 to 2015. A statistical tool like Pearson Product Moment Correlation (PPMC) is used in this study to establish the interrelationship and the level of impact and local climatic variation on dengue. An exceptional negative correlation value of r = -0.82 between the monsoon index and the dengue incidences was reported during the positive years and also maintains a very high positive correlation with other global climatic indices. The study here finds that there is a strong correlation of climatic variation which further influences the epidemiology of dengue in Delhi.

Atmosphere Driven Mass-Balance Sensitivity of Halji Glacier, Himalayas

The COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) was employed to investigate the relationship between the variability and sensitivity of the mass balance record of the Halji glacier, in the Himalayas, north-western Nepal, over a 40 year period since October 1981 to atmospheric drivers. COSIPY was forced with the atmospheric reanalysis dataset ERA5-Land that has been statistically downscaled to the location of an automatic weather station at the Halji glacier. Glacier mass balance simulations with air temperature and precipitation perturbations were executed and teleconnections investigated. For the mass-balance years 1982 to 2019, a mean annual glacier-wide climatic mass balance of −0.48 meters water equivalent per year (m w.e. a−1) with large interannual variability (standard deviation 0.71 m w.e. a−1) was simulated. This variability is dominated by temperature and precipitation patterns. The Halji glacier is mostly sensitive to summer temperature and monsoon-related precipitation perturbations, which is reflected in a strong correlation with albedo. According to the simulations, the climate sensitivity with respect to either positive or negative air temperature and precipitation changes is nonlinear: A mean temperature increase (decrease) of 1 K would result in a change of the glacier-wide climatic mass balance of −1.43 m w.e. a−1 (0.99m w.e. a−1) while a precipitation increase (decrease) of 10% would cause a change of 0.45m w.e. a−1 (−0.59m w.e. a−1). Out of 22 circulation and monsoon indexes, only the Webster and Yang Monsoon index and Polar/Eurasia index provide significant correlations with the glacier-wide climatic mass balance. Based on the strong dependency of the climatic mass balance from summer season conditions, we conclude that the snow–albedo feedback in summer is crucial for the Halji glacier. This finding is also reflected in the correlation of albedo with the Webster and Yang Monsoon index.

Analysing the Return Period and Risk under the Influence of Physical Covariates on Hydrological Extreme

&lt;p&gt;For sustainable water resources planning and management, it is necessary to redefine the concept of return period, risk, and reliability of hydrologic extreme under non-stationary condition. Thus, the present study aims to examine the return period, risk introducing physical based covariates in the location parameter of the generalised extreme value (GEV) distribution. The study is performed over the Godavari River basin, India. The expected waiting time (EWT) approach is used to make comparison of return period, risk between stationary and non-stationary approaches. From the analysis, it is found that 50% of the gauging stations are impacted by large scale modes/oscillations and regional hydrological variability, primarily by Indian Summer Monsoon Index (ISMI) and precipitation. The EWT interpretation estimates that the non-stationary return period, risk, and reliability are significantly different from stationary condition. Hence, it is concluded that return period analysis and risk assessment using non-stationary approach can be beneficial to water managers and policy makers in order to devise sustainable and resilient water resources infrastructure under climate change scenario.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; Extreme value analysis; Return period; Risk; Non-stationarity; Uncertainty&lt;/p&gt;

Impact of Indo-Pacific Climate Variability on High Streamflow Events in Mahanadi River Basin, India

The potential impact of climate variability on the hydrological regime in the Mahanadi river basin is of great importance for sustainable water resources management. The impact of climate variability on streamflow is analyzed in this study. The impact of climate variability modes on extreme events of Mahanadi basin during June, July, and August (JJA), and September, October, and November (SON) seasons were analyzed, with daily streamflow data of four gauge stations for 34 years from 1980 to 2013 found to be associated with the sea surface temperature variations over Indo-Pacific oceans and Indian monsoon. Extreme events are identified based on their persistent flow for six days or more, where selection of the stations was based on the fact that there was no artificially regulated streamflow in any of the stations. Adequate scientific analysis was done to link the streamflow variability with the climate variability and very significant correlation was found with Indian Ocean Dipole (IOD), El Nino Southern Oscillation (ENSO), El Nino Modoki Index (EMI), and Indian monsoon. Agriculture covers major portion of the basin; hence, the streamflow is very much essential for agriculture as well as population depending on it. Any disturbances in the general flow of the river has subjected an adverse impact on the inhabitants’ livelihood. While analyzing the correlation values, it was found that all stations displayed a significant positive correlation with Indian Monsoon. The respective correlation values were 0.53, 0.38, 0.44, and 0.38 for Andhiyarkore, Baronda, Rajim, and Kesinga during JJA season. Again in the case of stepwise regression analysis, Monsoon Index for the June, July, and August (MI-JJA) season (0.537 for Andhiyarkore) plays significant role in determining streamflow of Mahanadi basin during the JJA season and Monsoon Index for July, August, and September (MI-JAS) season (0.410 for Baronda) has a strong effect in affecting streamflow of Mahanadi during the SON season. Flood frequency analysis with Weibull’s plotting position method indicates future floods in the Mahanadi river basin in JJA season.

Understanding the Variability of West African Summer Monsoon Rainfall: Contrasting Tropospheric Features and Monsoon Index

West African Summer Monsoon (WASM) rainfall exhibits large variability at interannual and decadal timescales, causing droughts and floods in many years. Therefore it is important to investigate the major tropospheric features controlling the WASM rainfall and explore its potential to develop an objective monsoon index. In this study, monthly mean reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and monthly rainfall data from three gridded observations during the 65-year period of 1950–2014 were employed. Dry and wet rainfall years were identified using a standardized precipitation index. In a composite analysis of wet and dry years, the dynamical features controlling the WASM exhibit an obvious contrast between these years, and a weaker (stronger) African Easterly Jet (Tropical Easterly Jet) is observed during the wet years. Also, a well-developed and deep low-level westerly flow at about 850 hPa is evident in wet years while an obvious reversal is observed in dry years. Considering this, the main regions of the two easterly jet streams and low-level westerly wind are proposed for objectively defining an effective WASM index (WASMI). The results indicate that the WASMI defined herein can reflect variations in June–September rainfall over West Africa. The index exhibits most of the variabilities observed in the rainfall series, with high (low) index values occurring in the 1950–1960s (1970–1980s), suggesting that the WASMI is skilled in capturing the respective wet and dry rainfall episodes over the region. Also, the WASMI is significantly correlated (r = 0.8) with summer monsoon rainfall, which further affirms that it can indicate not only variability but also the intensity of WASM rainfall.