Rainfall Record Research Articles

Crop water requirement calculations of Longan (Dimorcapus longan L.) in Nawungan Orchard, Selopamioro Village, Imogiri Sub-District, Bantul, D.I. Yogyakarta

This research was aimed to measure actual evapotranspiration, to determine of water requirement and crop coefficient (Kc) of longan (Dimorcapus longan Lour.) was cultivated in Longan Nawungan orchard, Selopamioro Village, Imogiri Sub-district. Plot scale of water balance was applied to determine ETa, with input components were rainfall and irrigation, while output were ETa, water storage (ΔSM), and surface runoff (SRO). Components of runoff was measured using tank and the moisture content was measured using gravimetry method. Automatic weather station was installed in Nawungan orchard to record rainfall, wind speed, air humidity, and intensity of solar radiation. Later, the climatic data were used to calculate the reference evapotranspiration (ETo) using Penman-Monteith method. Due to agroforestry and mix cropping system, longan trees were cultivated among seasonal crops and other trees, then the dual crop coefficient (Kc) was preffered. During February-Maret 2019, the value of rainfall and surface runoff were 640 mm during observation period and 0,08 mm, respectively. The reference evapotranspiration (ETo) and actual evapotranspiration (ETa) were 5,76 mm/day and 7,90 mm/day, respectively. The crop coefficient of longan in the site study area was 0,30.

Crop water requirement of Soursop (Annona muricata L) in Nawungan orchard, Selopamioro village, Imogiri sub-district, Bantul regency, Yogyakarta

The aim of this study was to to measure actual evapotranspiration and to determine of water requirement and crop coefficient (Kc) of of soursop (Annona muricata L). The soursop was farmed at Nawungan orchard in Selopamioro village, Imogiri sub-district. Village monographs, 1: 25,000 scale Indonesian earth map and climate data were used to get the purpose of study. An Automatic Weather Station (AWS) was installed in Nawungan orchard to record rainfall, air relative humidity, wind velocity, solar radiation, as well as soil moisture every fifteen minutes. A set of surface runoff equipment was set in soursop farming land. Infiltration test was conducted in nine selected locations of soursop farming land and later, it was used to find soil percolation value. The purposive sampling method was adopted to assign the nine locations of infiltration test. The reference evapotranspiration (ET0) was calculated by the Penman-Monteith method. Later, water balance formula was applied to determine the actual plant water requirements (ETa) and plant coefficient value (Kc). This study proved the reference evapotranspiration (ET0) of the study area was 5.74 mm / day, the actual crop water requirement (ETa) of soursop was 7.98 mm / day. And Kc of soursop was 0.576.

Rainfall threshold for initiating effective stress decrease and failure in weathered tephra slopes

Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) deposits are especially vulnerable to slope failure because they commonly form slopes of high porosity and high clay content. Empirically derived thresholds for the triggering of landslides are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional variable for the threshold calibration. Here, we derived a new rainfall threshold for initiating the decrease in effective stress in the slope by analyzing a long-term record of rainfall and piezometer data from a slide-prone coastal area in northern New Zealand that consists of clayey, halloysitic tephra deposits. The level of effective stress decrease increased with rainfall intensity and duration. We observed highest effective stress decrease of up to 36% during rainfall events that triggered landslides in our study area. The effective stress threshold exhibits a satisfactory predictive capability. The probability of correctly predicting a decrease in effective stress is 53%. The effective stress threshold contributes towards the implementation of the decrease in effective stress into rainfall thresholds for the occurrence of landslides.

Snake Line Performance Applying Single Pixel X-Band MP Radar Data (Case of Mt. Merapi Area, Indonesia)

The short-duration-rainfall monitoring techniques have become important recently due to the high demand for disaster risk miti­gation. Such techniques produce important information on the rainfall intensity during heavy rainfall in the form of snake line. At the same time, use of X-Band Multi-Parameter Radar (XMP Radar) in rainfall monitoring has increased significantly be­cause of its capacity to cover wide area. An assessment on the snake line performance that was developed based on XMP Radar and ground rainfall monitoring instrument (i.e. Automatic Rainfall Recorder or ARR) has been applied to Mt. Merapi area, Java, Indonesia. Selected rainfall data of November-December 2018 were examined. The assessment used a single pixel of radar data at the location of the ARR. The result shows that rainfall data obtained from XMP Radar are lower than those from ARR. The computed snake line obtained from XMP Radar differs from that from ARR data. The XMP Radar underestimates the warning level by about two level out of four.

Update of the erosive rain factor in Slovakia using data from the period 1961–2009

Abstract An update of the rainfall erosivity factor (R-factor) estimated for 95 locations throughout the entire territory of Slovakia is presented in this paper. We analyzed rainfall time series with 1-minute resolution provided by the Slovak Hydrometeorological Institute. The data cover the period 1961–2009. The rain gauges are located at altitudes ranging from 97 m a.s.l. up to 1322 m a.s.l. and cover the broadest possible range of geographic regions and climatic conditions in Slovakia with reliable rainfall measurements. First, rainfall episodes were isolated by applying the fundamental rule that two subsequent rains are separated by at least six hours of no rainfall. A total of 116,710 rainfall events were identified and analyzed. A rainfall event was classified as erosive if the two following criteria were satisfied: the maximum 15-minute intensity 6.25 mm (i.e. 25 mm hr−1, as originally used in the U.S.L.E. model, and/or rainfall depth was greater than 12.5 mm. The presented estimates of R-factor are based on 18,467 identified erosive rainfall events. Furthermore, the minimum length of rainfall record necessary for reliable estimates of R-factor has been estimated by spectral analysis. The Lomb-Scargle periodogram identified periodic behavior of the total kinetic rainfall energy and rainfall 15-minute intensities. We suggest that these periodicities are attributable mainly to the 11-year Sun spot cycle, the 18.6-year Luni-Solar cycle, and their higher harmonics. The spectral analysis also revealed that in order to capture the temporal variability the minimum length of time-series in calculating R-factors is 14–15 years. We estimate that the long-term mean annual R-factor in Slovakia ranges from 34.8 MJ ha−1 cm hr−1 (at Gabčíkovo station) to 138 MJ ha−1 cm hr−1 (at Tatranská Javorina station). The median value of the mean annual R-factors for the whole country is 71.13 MJ ha−1 cm hr−1. To our best knowledge, the erosive rain factor has not been updated in Slovakia since the earlier work of Mišík in 1990. This paper is thus an update of the R-factors in Slovakia.

Rainfall variations in central Indo-Pacific over the past 2,700 y

Tropical rainfall variability is closely linked to meridional shifts of the Intertropical Convergence Zone (ITCZ) and zonal movements of the Walker circulation. The characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are, however, still unclear. Here, we reconstruct a replicated stalagmite-based 2,700-y-long, continuous record of rainfall for the deeply convective northern central Indo-Pacific (NCIP) region. Our record reveals decreasing rainfall in the NCIP over the past 2,700 y, similar to other records from the northern tropics. Notable centennial- to decadal-scale dry climate episodes occurred in both the NCIP and the southern central Indo-Pacific (SCIP) during the 20th century [Current Warm Period (CWP)] and the Medieval Warm Period (MWP), resembling enhanced El Niño-like conditions. Further, we developed a 2,000-y-long ITCZ shift index record that supports an overall southward ITCZ shift in the central Indo-Pacific and indicates southward mean ITCZ positions during the early MWP and the CWP. As a result, the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period, suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability.

Using Spatial Analysis to Examine Potential Sources of Polycyclic Aromatic Hydrocarbons in an Environmental Justice Community After Hurricane Harvey.

Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants associated with adverse human health outcomes. Environmental justice neighborhoods experience disproportionate environmental health risks. Hurricane Harvey made landfall on August 25, 2017, bringing record rainfall and catastrophic flooding to Houston, Texas, redistributing PAHs in residential soil. We aimed to describe PAH distributions in soil in the Manchester neighborhood of Houston, TX, and identify their potential sources. Soil samples were collected from 24 residential addresses and analyzed for 16 priority PAH concentrations using an accelerated solvent extractor. PAH distribution and source determination were conducted using spatial analysis and isomer ratios. All sample sites detected PAHs in soil, with the total mass ranging from 0.75 to 69.9 ng/g, which were predominantly four-ring structured PAHs. Total PAH concentrations were highest on the northeastern border of the neighborhood, whereas lower overall concentrations of PAHs were found on the southwestern border, at the highest elevation in the watershed. The ratio indeno[1,,3-cd]pyrene (IP) to indeno[1,,3-cd]pyrene plus benzo[ghi]perylene indicated vehicular combustion as the primary source in 19 of 23 samples. After heavy rainfall from Hurricane Harvey in the Manchester neighborhood, PAHs in soil were unevenly distributed throughout the neighborhood, with an accumulation of PAHs in the northeastern edges. Using isomer ratios and spatial analysis, the likely source of PAHs is from use of transportation infrastructure.

Analysis of Rainfall Variability in Sylhet Region of Bangladesh

The variability and distributions of rainfall of a region is important and useful especially for agricultural activities. The study was conducted to establish the rainfall trends in Sylhet by analyzing available rainfall record for 35 years period of 1981 to 2015. Records of daily rainfall data for Sylhet region were obtained from the Bangladesh Meterological Department (BMD) for analysis. Rainfall data were categorized into monthly, annual, and seasonal basis. The rainfall pattern was studied by statistical analysis and graphical illustration. The mean, standard deviation and coefficient of variation of annual and monthly rainfall was calculated to understand the rainfall variability. Linear regression analysis revealed downward trend in the data in some months and years but statistically insignificant. From the calculated results, the rainfall pattern is found to be erratic and decreasing pattern. Further, various plotting position formulae available was used to evaluate annual rainfall for various return periods. This analysis will provide necessary information for water resources engineers, planners, and farmers to evaluate the water availability and necessary storage accordingly.

The Influence of Geographical Factors on Extreme Rainfalls in Lampung Province

Many people in Indonesia calculate design rainfall before calculating the design flooddischarge. The design rainfall with a certain return period will eventually be convertedinto a design flood discharge by combining it with the characteristics of the watershed.However, the lack of a network of rainfall recording stations makes many areas that arenot hydrologically measured (ungauged basin), so it is quite difficult to know thecharacteristics of rain in the area concerned. This study aims to analyze thecharacteristics of design rainfall in Lampung Province. The focus of the analysis is toinvestigate whether geographical factors influence the design rainfall that occurs in theparticular area. The data used in this study is daily rainfall data from 15 rainfallrecording stations spread in Lampung Province. The method of frequency analysis usedin this study is the Gumbel method. The research shows that the geographical location ofan area does not have significant effect on extreme rainfall events. The effect of risingearth temperatures due to natural exploitation by humans tends to be stronger as a causeof extreme events such as extreme rainfall.Keywords: Influence, geographical, factors, extreme, rainfall.

Observing Hurricane Harvey’s Eyewall at Landfall

AbstractWhile Hurricane Harvey will best be remembered for record rainfall that led to widespread flooding in southeastern Texas and western Louisiana, the storm also produced some of the most extreme wind speeds ever to be captured by an adaptive mesonet at landfall. This paper describes the unique tools and the strategy used by the Digital Hurricane Consortium (DHC), an ad hoc group of atmospheric scientists and wind engineers, to intercept and collect high-resolution measurements of Harvey’s inner core and eyewall as it passed over Aransas Bay into mainland Texas. The DHC successfully deployed more than 25 observational assets, leading to an unprecedented view of the boundary layer and winds aloft in the eyewall of a major hurricane at landfall. Analysis of anemometric measurements and mobile radar data during heavy convection shows the kinematic structure of the hurricane at landfall and the suspected influence of circulations aloft on surface winds and extreme surface gusts. Evidence of mesoscale vortices in the interior of the eyewall is also presented. Finally, the paper reports on an atmospheric sounding in the inner eyewall that produced an exceptionally large and potentially record value of precipitable water content for observed soundings in the continental United States.

Evaluation of spatio‐temporal rainfall variability and performance of a stochastic rainfall model in Bangladesh

Rainfall in Bangladesh exhibits persistent wet and dry anomalies associated with occurrence of floods and droughts. Assessing inter‐annual variability of rainfall is vital to account these hydrological extremes in the design and operations of water systems. However, the inter‐annual variability obtained from short record rainfall data might be misleading as it does not contain whole climate variability which signifies the utmost importance of stochastic rainfall models. Since the inter‐annual variability and stochastic models have not been explored adequately for rainfall in Bangladesh, this study evaluated (a) the spatio‐temporal variability of rainfall focusing on inter‐annual variability, and (b) applicability of a stochastic daily rainfall model, referred as the Decadal and Hierarchical Markov Chain (DHMC) model. Daily rainfall data of 1973–2012 for 18 stations across Bangladesh were used to investigate the probability distributions and autocorrelations of rainfall, and the model performances. Results show a higher magnitude of inter‐annual variabilities of rainfall depth (standard deviation 80–250 mm) and wet spells (standard deviation 4–6 days) in wetter months (June to September) across rainfall stations in the east region of the country. In contrast, higher rates of inter‐annual variabilities (i.e., coefficients of variations) were observed in drier months across the west region. Spatially, the dry spells were observed consistent across the country. Monthly rainfall showed decreasing trend over the region from west to the middle part of the country, whereas monthly number of wet days showed increasing trend over the eastern part. The DHMC was found to preserve the observed variabilities of rainfall at daily to multiyear resolutions at all stations, except a tendency to underestimate the autocorrelation of monthly rainfall depth. Despite this limitation, DHMC can be considered as a suitable stochastic rainfall simulator for a tropical monsoon climate like Bangladesh.

Land subsidence in Houston correlated with flooding from Hurricane Harvey

Hurricane Harvey caused unprecedented flooding and socioeconomic devastation in Eastern Texas with high winds, elevated storm tide, and record rainfall. The flooded area is mapped using the radar backscattering difference between Sentinel-1A/B satellite acquisitions spanning the event, which provides a snapshot of standing water at the time of image acquisition. We find vast areas outside of designated flood hazard zones are overwhelmed. Furthermore, we map pre-cyclone land subsidence using multitemporal interferometric processing of large SAR datasets acquired by Advanced Land Observation Satellite (ALOS) and Sentinel-1A/B satellites. We find that subsidence of up to 49 mm/yr and 34 mm/yr during the ALOS (Jul-2007–Jan-2011) and Sentinel-1A/B (Dec-2015 to Aug-2017) acquisition periods affect various parts of Houston-Galveston area. We conclude that 85% of the flooded area subsided at a rate > 5 mm/yr. We suggest that subsidence affected flood severity by modifying base flood elevations and topographic gradients, supported by the Chi-square test of independence. This work highlights the importance of incorporating InSAR measurements of land subsidence in flood resilience strategies.

An analysis of characteristic discharges for the Adaim River (Iraq) in multiyear period

AbstractA major River Tigris tributary in Iraq, the Adaim River, has a Mediterranean river flow regime with a total basin area of 12,482 km2. The river catchment responds almost immediately to rainfall with apparently minimum storage (i.e. flashy stream). The river daily hydrograph showed a daily peak flow of 1,476 m3/s with substantial seasonal and random variability; the flow duration curve followed the two‐parameter lognormal probability distribution. Gamma and the two‐parameter Weibull probability distributions fitted the monthly mean river discharge for the period 1937–2012 well. Normal and gamma probability distributions were found to appropriately describe the distribution of the annual mean river discharge for the same period. Gumbel extreme value, Log Pearson type III, and the two‐parameter lognormal distributions gave a reasonable fit to the annual maximum discharge record for the river. A regression formula was used to fit the annual minimum discharge record, which has a significant number of zero values. There was a positive and significant correlation (r = 0.77) between the annual mean discharge at the measuring site and seasonal rainfall measured at Karkuk meteorological station located in the north central part of the basin. The rainfall record at Karkuk showed a significant decline in seasonal rainfall after 1993.

Comparing Multiple Precipitation Products against In-Situ Observations over Different Climate Regions of Pakistan

Various state-of-the-art gridded satellite precipitation products (GPPs) have been derived from remote sensing and reanalysis data and are widely used in hydrological studies. An assessment of these GPPs against in-situ observations is necessary to determine their respective strengths and uncertainties. GPPs developed from satellite observations as a primary source were compared to in-situ observations, namely the Climate Hazard group Infrared Precipitation with Stations (CHIRPS), Multi-Source Weighted-Ensemble Precipitation (MSWEP), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) and Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA). These products were compared to in-situ data from 51 stations, spanning 1998–2016, across Pakistan on daily, monthly, annual and interannual time scales. Spatiotemporal climatology was well captured by all products, with more precipitation in the north eastern parts during the monsoon months and vice-versa. Daily precipitation with amount larger than 10 mm showed significant (95%, Kolmogorov-Smirnov test) agreement with the in-situ data, especially TMPA, followed by CHIRPS and MSWEP. At monthly scales, there were significant correlations (R) between the GPPs and in-situ records, suggesting similar dynamics; however, statistical metrics suggested that the performance of these products varies from north towards south. Temporal agreement on an interannual scale was higher in the central and southern parts which followed precipitation seasonality. TMPA performed the best, followed in order by CHIRPS, MSWEP and PERSIANN-CDR.

A review of past and projected changes in Australia's rainfall

There has been much attention given to the spatial and temporal characteristics of changes in mean and extreme rainfall over Australia during the past century. As Australia is the second driest continent on Earth, reliable projections around the trends and variability in future rainfall are crucial for policymakers and water resource management. This article comprehensively reviews the current published literature on trends in Australia's rainfall from pre‐instrumental and instrumental records, the climatic drivers of Australia's rainfall variability, attribution of the long‐term trends, extreme rainfall attribution methods with particular reference to a recent case study (2010–2012 east Australia rainfall event) and projected changes of mean and extreme rainfall over Australia during the 21st century. Notable trends in the observational record of rainfall in Australia are a decrease in mean rainfall in southwest and southeast Australia and an increase in northwest Australia since 1950. The general consensus of research into Australia's future rainfall is that mean rainfall will continue to decrease in southwest Australia in a warming world, while changes over northern and eastern Australia remain uncertain. There are still significant knowledge gaps around the causes of observed trends in rainfall both in the mean and extremes, the ability of climate models to accurately represent rainfall in the Australian region and future rainfall projections. These gaps are identified, and avenues for future research directions are proposed.This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change

A shift from drought to extreme rainfall drives a stable landslide to catastrophic failure

The addition of water on or below the earth’s surface generates changes in stress that can trigger both stable and unstable sliding of landslides and faults. While these sliding behaviours are well-described by commonly used mechanical models developed from laboratory testing (e.g., critical-state soil mechanics and rate-and-state friction), less is known about the field-scale environmental conditions or kinematic behaviours that occur during the transition from stable to unstable sliding. Here we use radar interferometry (InSAR) and a simple 1D hydrological model to characterize 8 years of stable sliding of the Mud Creek landslide, California, USA, prior to its rapid acceleration and catastrophic failure on May 20, 2017. Our results suggest a large increase in pore-fluid pressure occurred during a shift from historic drought to record rainfall that triggered a large increase in velocity and drove slip localization, overcoming the stabilizing mechanisms that had previously inhibited landslide acceleration. Given the predicted increase in precipitation extremes with a warming climate, we expect it to become more common for landslides to transition from stable to unstable motion, and therefore a better assessment of this destabilization process is required to prevent loss of life and infrastructure.

Estimation of Peak Discharge in a Poorly Gauged Catchment Based on a Specified Hyetograph Model and Geomorphological Parameters: Case Study for the 23–24 October 2008 Flood, KALAYA Basin, Tangier, Morocco

The determination of discharge from stage measurement is an essential procedure in surface hydrology. Due to limited data availability in terms of discharges and rainfalls, a number of non-flood water levels have been used for deriving a rating curve based on an indirect method with specific cross-sections, longitudinal slope of the river, and bed roughness at the KALAYA gage station. In addition, instantaneous rainfall recordings across the Meloussa gage station are available from 23 October 2008 storm event that have been collected in order to develop temporal distribution (hyetograph). Thereby, it provides the necessary input to generate a continuous rainfall-runoff time series, with the derived instantaneous discharge allowed us to calibrate the simulated stage-discharge hydrograph that covers the entire time of the storm event period from 23 to 24 October. An empirical equation was derived in order to provide the peak flow as a function of the given rainfall quantities, its standard deviation, and its standard deviation error. As a result, a very positive correlation between Runoff and Rainfall was observed with values of 0.999. Additional tests were performed to generate a peak discharge of approximately 486 m3/s, using the observed hyetograph and calibrating CN, Lagtime, and Initial abstraction. The results would improve the quality of the model since it allows for a more precise hyetograph to be simulated over a smaller area.

Overcoming data scarcity in flood hazard assessment using remote sensing and artificial neural network

Many urban cities in Southeast Asia are vulnerable to climate change. However, these cities are unable to take effective countermeasures to address vulnerabilities and adaptation due to insufficient data for flood analysis. Two important inputs required in flood analysis are high accuracy Digital Elevation Model (DEM), and long term rainfall record. This paper presents an innovative and cost-effective flood hazard assessment using remote sensing technology and Artificial Neural Network (ANN) to overcome such lack of data. Shuttle Radar Topography Mission (SRTM) and multispectral imagery of Sentinel-2 are used to derive a high-accuracy DEM using ANN. The improvement of SRTM’s DEM is significant with a 42.3% of reduction on Root Mean Square Error (RMSE) which allows the flood modelling to proceed with confidence. The Intensity Duration Frequency (IDF) curves that were constructed from precipitation outputs from a Regional Climate Model (RCM) Weather Research and Forecasting (WRF) were used in this study. Design storms, calculated from these IDF curves with different return periods were then applied to numerical flood simulations to identify flood prone areas. The approach is demonstrated in a flood hazard study in Kendal Regency, Indonesia. Flood map scenarios were generated using improved SRTM and design storms of 10-, 50- and 100-year re-turn periods were constructed using the MIKE 21 hydrodynamic model. This novel approach is innovative and cost-effective for flood hazard assessment using remote sensing and ANN to overcome lack of data. The results are useful for policy makers to understand the flood issues and to proceed flood mitigation adaptation/measures in addressing the impacts of climate change.

A comparison of weather systems in 1870 and 1956 leading to extreme floods in the Murray–Darling Basin

This research is the extension of a project studying the impact of 19th century severe weather events in Australia and their relation to similar events during the 20th and 21st century. Two floods with the worst known impacts in the Murray–Darling Basin (MDB) are studied. One of these events which occurred during 1956 is relativelywell known and the Bureau of Meteorology archives contain good rainfall data covering the period. Additionally, information on the weather systems causing this rainfall can be obtained. Rainfall, flood and weather system data for this event are presented here and compared with a devastating event during 1870. Although archived Australian rainfall data is negligible during 1870 and there is no record of weather systems affecting Australia during that year, a realistic history of the floods and weather systems in the MDB during 1870 is created. This follows an extensive search through newspaper archives contained in the National Library of Australia’s web site. Examples are presented showing how the meteorological data in 19th century newspapers can be used to create weather charts. Six such events in 1870 are demonstrated and three of these had a phenomenal effect on the Murray–Darling system. The 1870 floods followed drought type conditions and it is remarkable that it was worse in many ways than the 1956 event which followed flood conditions in the MDB during the previous year. The events in 1870 caused much loss of life from drowning in the MDB in particular froman east coast low (ECL) in April 1870 and two Victorian weather systems in September and October 1870. In 1956, there were also record-breaking events especially during March when all-time record monthly rainfall were reported in New South Wales. Overall the greatest impact from flooding across the whole MDB was associated with the 1870 flooding. Analyses of heavy rainfall areas in the MDB showed a linear trend increase from 1900 to 2018. Analysing the same data using an 8-year moving average highlighted three peaks around the five highest annual rainfall years. The largest peak occurred around 1950 and 1956, the second largest around 1973 and 1974 and the third around 2010. Each of these 5 years occurred during negative phases of the Interdecadal Pacific Oscillation (IPO) and positive phases of the Southern Oscillation Index (SOI). Studies have shown that the SOI is a climate driver in the MDB along with a persistent blocking high-pressure systems south of Australia along longitude 140°E with a low to its north. Three major blocking events with record rainfall and flooding in the MDB occurred in 1983, 1984 and 1990. Thiswas during the period 1977–1990 when blocking was conducive to heavy rain in the MDB and was coincidentwith a positive phase of the IPO, thus helping conflictwith the IPO–MDB heavy rainfall relationship. Persistent and unexplained middle level westerly winds kept subtropical Queensland clear of tropical cyclones during the negative phases of the IPO from 1999 to 2009 and during the 1960s, influencing low rainfall in the MDB during those periods.

Rainfall Distribution Pattern of Progo Watershed in Observational and Empirical Method

Automatic Rainfall Recorder (ARR) has not been widely available in Indonesia, so data of rainfall is available in the form of daily rainfall. To know the pattern of rainfall distribution in a watershed, there are two methods, they are the observational and empirical method. the Observational Method can be done if it has automatic rainfall data minimal hourly-time in a long period. Meanwhile, the empirical method will be used when data is very limited. So in this research, there were two methods to develop the rainfall distribution pattern in Progo Watershed. The data were used by the observational method is from 2013 to 2015. There were two empirical methods which are used namely Alternating Block Method (ABM) and Modified Mononobe Method. The results show that heavy rainfall in Progo watershed is dominated by 7-hourly rainfall distribution. The empirical rainfall distribution pattern that is more suitable with the observation method is Modified Mononobe method than ABM method.