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Abstrak :
Rainfall is the primary input into rainfall-runoff modeling. Previous work indicates that the accurate representation of rainfall in time and space is important due to its influence on the hydrological response. The objective of this study is to evaluate the relevance of theoretical indices of spatial rainfall variability and the theoretical criteria of the hydrological response proposed by Emmanuel et al. (2015) in a real case study. The distributed model CINECAR has been chosen to accommodate the spatial discretization of hydrological data. The production function of the model adopts the Soil Conservation Service-Curve Number method, while the transfer function is based on a kinematic wave model. The simulations used weather radar data and also their average over the watershed, with a data resolution of 1×1 km2. They were conducted on the basis of 13 watersheds in the Gard region and four events in 2008 for each watershed. The difference between the distributed and averaged hydrographs obtained from the CINECAR model were calculated using two criteria, namely the difference in peak discharge (LQ) and the difference in peak time (TQ). The values of LQ and TQ represent the influence of spatial rainfall variability on the hydrological response. The spatially distributed rainfall was analyzed based on the values of its maximum Horizontal and Vertical Gab (HG and VG) to watershed centroid acting as indices, as proposed by Emmanuel. The analysis of the influence of spatial rainfall variability on the watershed response was conducted by quantification of the averaged and distributed hydrographs using the proposed indices and criteria. The results show that value of LQ rises by more than 50% for some events, and that TQ shows different times to peak between the average and distributed hydrographs. The values of the HG and VG indices accurately describe the rainfall distribution in the watershed. Therefore, these criteria and indices are effective in quantifying the influence of spatial rainfall variability on the hydrological modeling in particular events which are affected by rainfall distribution.

Abstrak :
Pulau Bintan adalah Pulau kecil dengan batuan penyusun pulau didominasi oleh granit dan batupasir tufa yang mempunyai daya-simpan dan kelulusan air rendah. Variabilitas curah hujan adalah faktor utama dalam menentukan ketersediaan air di Pulau Bintan. Saat ini aktifitas perekonomian dan tingkat pertumbuhan penduduk tinggi, sehingga kebutuhan air meningkat cepat, yang mengakibatkan terjadi ketidak-seimbangan antara ketersediaan dan kebutuhan air. Curah hujan musiman di Indonesia terutama disebabkan oleh sistem Angin musim-Asia dan Angin musim-Australia, yang menyebabkan adanya musim kemarau dan musim hujan dengan durasi masing-masing musim 6 bulan dalam siklus satu tahun. Akan tetapi lama musim kemarau dan hujan tidak selalu sama setiap tahun, akibat ENSO dan IOD. Pulau Bintan secara geografis berada di sekitar ekuator, puncak hujan terjadi dua kali dalam setahun, seharusnya air yang tersedia cukup memadai. Faktor yang diduga mempengaruhi berkurangnya ketersediaan air adalah faktor fenomena iklim ENSO dan IOD. Studi ini melakukan analisis spasial dan temporal pengaruh fenomena iklim ENSO dan IOD pada ketersediaan air. Metodologi yang digunakan adalah analisis korelasi, komposit, Standar Precipitation Index serta pendugaan kuantitas sumberdaya air. Menggunakan data satelit CHIRPS skala detil, diharapkan memberikan informasi detil pengaruh fenomena iklim terhadap variabilitas curah hujan. Hasil penelitian menunjukkan fenomena iklim El-Niño dan IOD kuat mempengaruhi variabilitas curah hujan berdasarkan musim, mengakibatkan berkurangnya curah hujan yang mengakibatkan kekeringan meteorologi dan kelangkaan sumberdaya air. Untuk mengurangi dampak bencana akibat fenomena iklim, disarankan untuk menambah tampungan air hujan serta mengendalikan tutupan lahan, mengingat Pulau Bintan sangat sensitif terhadap fenomena iklim. Hasil penelitian diharapkan menjadi informasi penting dalam penentuan kebijakan pengelolaan sumberdaya air yang terarah dan terukur di Pulau kecil wilayah Ekuator, terutama yang berada di wilayah Belahan Bumi Utara Bagian Barat daya Indonesia. ......Bintan Island is a small island dominated by granite and tuff sandstones which mostly have low water-storage and water-permeability. Rainfall variability is the main factor in water availability determining on Bintan Island. Currently, economic activity and population growth rates are high, so that water demand is increasing rapidly, resulting in an imbalance between water supply and demand. Seasonal rainfall in Indonesia is mainly caused by the Monsoon-Asia and Monsoon-Australia systems, which cause dry and rainy seasons with a duration of 6 months each in oneyear cycle. However, the duration of the dry and rainy seasons is not always the same every year, due to ENSO and IOD. Bintan Island is geographically located around the equator; the peak of the rain occurs twice a year. With this condition, the water availability should be sufficient. The factors that are suspected to influence the reduced water availability are climate factors namely ENSO and IOD. This study has conducted the spatial and temporal analysis of the influence of ENSO and IOD climate phenomena on water resource availability. The methodology used is correlation and composite rainfall analysis, Standard Precipitation Index, and water resources quantity estimation. This study uses CHIRPS satellite data on a detailed scale, which is expected to provide detailed information on climate phenomena' s influence on rainfall variability. The results showed that the El Niño and IOD climatic phenomena affect rainfall variability based on seasons, resulting in the meteorological drought that is resulting in water resource scarcity. To reduce the impact of disasters due to climatic phenomena, it is recommended to add rainwater storage (retarded basin) and land cover controling, considering that Bintan Island is very sensitive to climate phenomena. The results of this study are expected to be used in water resource management policies of the equatorial small island, especially for small islands in the Northern Hemisphere, southwestern part of Indonesia.

Abstrak :
ABSTRAK
Keakuratan data hujan secara spasial dan temporal merupakan faktor yang penting dalam model hidrologi, terutama dalam prediksi banjir dan sistem peringatan dini banjir . Radar memberikan informasi yang lebih detail secara spasial dan temporal yang tidak dapat diperoleh dari stasiun hujan. Penelitian tentang pengaruh sebaran spasial hujan telah diteliti lebih dari 40 tahun yang lalu, akan tetapi masih menghasilkan kesimpulan yang kontradiktif. Guillermo., et al., 1985 menyatakan bahwa data sebaran hujan secara spasial dibutuhkan dalam studi hidrologi antara lain pada analisis neraca air, prediksi aliran melalui model hujan-aliran dan model hidrometeorologi. Anquetin., et al., 2010 , Tramblay., et al., 2011 , dan Zoccatelli., et al., 2010 mengulas bahwa sebaran spasial hujan faktor yang sangat penting dalam respon hidrologi. Sebaliknya, penelitian dari D.Tetzlaff., et al., 2005 , Nicotina., et al., 2008 , Adams., et al., 2012 dan Cristiano., et al., 2016 menyatakan bahwa pola hujan dan sebaran hujan bukan merupakan faktor penting yang mempengaruhi respon hidrologi. Emmanuel., et al., 2015 meneliti lebih lanjut pengaruh sebaran spasial hujan pada respon hidrologi daerah tangkapan air DTA hipotetik menggunakan model hidrologi spasial, dimana 900 variasi peristiwa hujan hipotetik disimulasikan pada 11 variasi konfigurasi DTA hipotetik. Berdasarkan hasil simulasi 9900 kombinasi peristiwa hipotetik tersebut, Emmanuel., et al mengusulkan dua indeks yang dapat menggambarkan pengaruh sebaran spasial hujan pada respon hidrologi DTA hipotetik yaitu : VG: vertical gab; HG: horizontal gab.Penelitian ini difokuskan pada kondisi riil daerah tangkapan air DTA , khususnya untuk peristiwa-peristiwa hujan lebat yang menghasilkan banjir bandang, dengan tujuan: untuk mengevaluasi kinerja indeks pengaruh sebaran spasial hujan yang diusulkan oleh Emmanuel et al, mengusulkan modifikasi indeks pengaruh sebaran spasial hujan yang diusulkan oleh Emmanuel et al., berdasarkan optimasi hasil simulasi, mensintesis relevansi indeks pengaruh sebaran spasial hujan yang dimodifikasi pada model hidrologi lump hidrograf satuan .Hasil yang diperoleh dari simulasi sangat tergantung pada sebaran spasial hujan dan intensitasnya. Untuk beberapa peristiwa hujan tersebar merata, debit puncak banjir untuk hujan dengan sebaran merata mendekati debit banjir hujan tersebar spasial. Untuk beberapa peristiwa hujan, perbedaan antara dua keadaan tersebut dapat mencapai lebih dari 50 . Perhitungan dari kriteria dapat menggambarkan dengan baik sebaran spasial hujan dan mengindikasikan tipe dari sebaran spasial yang dapat mempengaruhi respon suatu DTA. Untuk kejadian yang diwakili oleh DTA Ales pada tanggal 19 Oktober 2008, pengaruh sebaran spasial hujan terlihat siknifikan, hal ini direpresentasikan dengan baik oleh indeks dan kriteria. Nilai indeks dan kriteria sesuai dengan teori yang diusulkan. Akan tetapi pada peristiwa hujan merata, nilai indeks dan kriteria tidak sesuai. Pada saat nilai VG mendekati nol spasial dan merata dapat diabaikan akan tetapi nilai dari kriteria LQ tidak dapat diabaikan 25 . Hal ini menunjukan bahwa ada parameter lain yang juga mempengaruhi respon hidrologi pada suatu DTA. Hasil simulasi indeks yang diusulkan oleh Emmanuel et.al menunjukkan bahwa untuk beberapa hujan yang tersebar merata tidak menghasilkan kesesuaian antara indeks dan kriteria akibat pengabaian parameter fisik DTA. Penambahan karakteristik DTA pada perhitungan indeks menghasilkan kesesuaian antara indeks dengan kriteria. Pernggunaan hujan efektif pada perhitungan indeks disimulasikan baik pada kondisi hujan spasial maupun hujan merata. Perhitungan hujan efektif dilakukan berdasarkan metode SCS-CN. Indeks yang diusulkan oleh Emmanuel et.al dapat menggambarkan pengaruh sebaran spasial hujan pada respon hidrologi DTA dengan kondisi hipotetik. Akan tetapi pada kondisi riil, kinerja indeks tersebut tidak optimum. Dengan modifikasi indeks pengaruh sebaran hujan yang memperhitungkan karakteristik fisik DTA, menghasilkan kinerja yang optimum untuk mengases pengaruh sebaran spasial hujan pada respon hidrologi. Sintesis indeks pengaruh sebaran hujan pada lump model HSS Nakayasu mengindikasikan bahwa pada peristiwa hujan yang tersebar secara spasial spatialy distributed , model ini tidak relevan.

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ABSTRACT
Rainfall is the main input in the hydrological modeling. Accurate representation of rainfall in time and space is essential for rainfall-runoff modeling because it affects the hydrological responses. Many researchers have been observing the influence of spatial rainfall variability since many years ago, however the contradictive result still obtained. Various studies compare the performance of hydrological models obtained from different rainfall type in order to introduce the influence of rainfall measurement errors in hydrology.The consideration of spatial rainfall variability in hydrological modeling is not only an important scientific issue for researcher, but also requests from managers of urban sewage networks or hydrologic services who have interest about real time weather radar images. In order to get accurate rainfall data in time and space, the study about weather radar images has been developing detailed knowledge on rainfall spatial variability which is not available with rain gauge networks. Several researches have been developing study about the quality of weather radar measurement and the benefit of using weather radar observation.In order to predict the surface runoff on the whole system, it is necessary to use advance calculation and modeling techniques. Many hydrological models have been developed to simplify that conceptual. Based on the time scale hydrological models can be classified into event-based and continuous simulation. Event based is focus on determining runoff responses from single storm rainfall event . The advantageous are important for design and forecasting purposes and simplified the process descriptions less physical basis .Concerning on the analysis of influence of rainfall spatial variability on the watershed response, the rainfall variability Indices have been used to stratify the analysis. Several distributed modelling studies have considered the impact of spatial rainfall variability on modelled hydrograph. Spatial rainfall variability index was developed in order to explain the impact of spatial rainfall variability on the hydrological response. This research was focused on the real catchment area at Gard Region wich have intens rainfall event that caused flash flood. Based on the previouse research, the objective of this research are:To evaluate the performance of theoretical index of Emmanuel et al that already shown the good explanation of spatial rainfall variability on the simulated watershed and rainfall . Since the watershed parameter and rainfall are uncontrollable in the real condition, the performance of those Indices will be difference also.To propose the indexed modification based on the result of the real case study Indices simulation.To synthesize the relevance of the Indices on the lump model according to the observation data. The distributed model CINECAR has been chosen to accommodate the spatial discretization of hydrological data. The production function of the model adopts the Soil Conservation Service-Curve Number method, while the transfer function is based on a kinematic wave model. The simulations used weather radar data and also their average over the watershed, with a data resolution of 1 1 km2. They were conducted on the basis of 13 watersheds in the Gard region and four events in 2008 for each watershed. The difference between the distributed and averaged hydrographs obtained from the CINECAR model were calculated using two criteria, namely the difference in peak discharge LQ and the difference in peak time TQ . The values of LQ and TQ represent the influence of spatial rainfall variability on the hydrological response. The spatially distributed rainfall was analyzed based on the values of its maximum Horizontal and Vertical Gab HG and VG to watershed centroid acting as indices, as proposed by Emmanuel. Since the simulation of the proposed Indices do not have the satisfactory result on some rainfall event, the modification of their Indices needed to get the better analyze about the influence of spatial rainfall variability. The modification Indices computation, the effective rainfall calculation has been done by considering to SCS-CN method over the catchment. The effective rainfall calculated both on the average and distributed rainfall data. The result of several simulation of modification index shown the better performance on the real case study than the previous index.Since in Indonesia has a limitation on the distributed rainfall data, lumped conceptual modelling that represent on the unit hydrograph over the catchment can accommodate that limitation. The Nakayasu method, a synthetic unit hydrograph method that often used to calculate the peak discharge in Indonesia. In this case, nakayasu computation will be applied on the gard region in order to discover the difference when using the distributed hydrological model and lump model. Nakayasu method will represent the averaged method of hydrological model. With the assumption that the data which obtained from Indices calculation is a normal distribution data, the average value of VG can provide a max discharge of lump model close to the max discharge of distributed model.

Abstrak :
Curah hujan merupakan salah satu unsur iklim yang sangat bervariasi, baik dalam skala ruang maupun waktu. Variasi curah hujan ini berdampak pada penentuan awal masa tanam khususnya tanaman padi. Melalui penghitungan statistik dan pemetaan data spasial, penelitian ini akan mengungkapkan pola awal musim tanam sebagai respon terhadap variabilitas curah hujan di Kabupaten Kebumen selama periode tiga puluh tahun, yaitu tahun 1981 - 2010. Analisis spasial yang diperkuat dengan pendekatan statistik mengungkapkan bahwa wilayah pesisir di Kabupaten Kebumen memiliki variabilitas curah hujan yang tinggi dengan rata rata curah hujan rendah. Semakin tinggi tempat, variabilitas curah hujannya semakin menurun diikuti rata-rata curah hujan yang semakin tinggi. Selain itu, Awal musim tanam padi dimulai pada wilayah dengan variabilitas curah hujan yang rendah (perbukitan) menuju wilayah variabilitas curah hujan tinggi (pesisir). Pada periode 1981 - 2000, awal musim tanam padi dimulai dari utara dan bergerak menuju Selatan Kabupaten Kebumen. Sedangkan pada periode 2001-2010, awal musim tanam padi dimulai dari barat laut dan bergerak menuju tenggara dan selatan Kabupaten Kebumen.

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Rainfall is one element of climate that varied, both in space and time scale. These variations of rainfall affect the beginning of paddy growing season. Through a statistical calculation and mapping of spatial data, this research reveal a pattern of early growing season in response to rainfall variability in Kebumen Regency over a period of thirty years from 1981 to 2010. Spatial analysis with a reinforced approach statistics reveal that the coastal region in Kebumen Regency has high rainfall variability with an average of rainfall is low. The higher variability of annual precipitation, followed by the higher rainfall. In addition, the beginning of paddy planting season from the areas with low rainfall variability (the hills) to the region's high rainfall variability (coastal). In the period 1981-2000, paddy planting season move from the North and South Kebumen Regency. While from 2001-2010, paddy planting season move from Northwest to the Southeast and South Kebumen Regency.