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Assessment of agricultural drought based on CHIRPS data and SPI method over West Papua - Indonesia

Faisol Arif, Indarto Indarto, Novita Elida, Budiyono Budiyono

Journal of Water and Land Development

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2022

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no. 52

44--52

EN

This study aims to utilise Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) data and Standardised Precipitation Index (SPI) method to assess agricultural drought in West Papua, Indonesia. The data used in this study is monthly CHIRPS data acquired from 1996 to 2019, daily precipitation data recorded from 1996 to 2019 from the five climatological stations in West Papua, Indonesia located at Sorong, Fakfak, Kaimana, Manokwari, and South Manokwari. 3-month SPI or quarterly SPI are used to assess agricultural drought, i.e., SPI January-March, SPI February-April, SPI March-May, SPI April-June, SPI May-July, SPI June-August, SPI July-September, SPI August-October, SPI September-November, and SPI October-December. The results showed that in 2019 agricultural drought in West Papua was moderately wet to severely dry. The most severely dry occurred in September-December periods. Generally, CHIRPS data and SPI methods have an acceptable accuracy in generating drought information in West Papua with an accuracy of 53% compared with climate data analysis. Besides, the SPI from CHIRPS data processing has a moderate correlation with climate data analysis with an average R2= 0.51.

2

Modelling erosion and sedimentation in a small watershed, East Java, Indonesia

Sujarwo Mohamad Wawan, Indarto Indarto, Mandala Marga

Journal of Water and Land Development

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2021

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no. 50

265--273

EN

Changes in land use as a result of human activities may generate the alteration of hydrometeorological disasters. Erosion, sedimentation, floods and landslides frequently occur in the Sanenrejo watershed (±292 km2), located in East Java, Indonesia. In this paper, the soil and water assessment tool (SWAT) model is used to evaluate the hydrological processes in this small watershed. The digital elevation model (DEM) is used as the primary input for deriving the topographic and physical properties of the watershed. Other input data used for the modelling processes include soil type, land use, observed discharge data and climate variables. These data are integrated into the SWAT to calculate discharge, erosion and sedimentation processes. The existing observed discharge data used to calibrate the SWAT output at the watershed outlet. The calibration results produce Nash–Sutcliffe efficiency (NSE) of 0.62 and determination coefficient (R2) of 0.75, then the validation result of 0.5 (NSE) and 0.63 (R2). The middle area faced the highest erosion and sedimentation that potentially contribute to hydrometeorological disasters.

3

Comparing automatic baseflow separation filters on three watersheds in the urbanised area of East Java, Indonesia

Indarto Indarto, Hardiansyah Mujiono, Sujarwo Mohamad Wawan

Journal of Water and Land Development

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2021

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no. 50

130--140

EN

Baseflow is the primary source of water for irrigation and other water needs during prolonged dry periods; accurate and rapid estimation of baseflow is therefore crucial for water resource allocation. This research aims to estimate baseflow contribution during dry periods in three small watersheds in East Java: Surabaya-Perning (114 km2), Lamong-Simoanggrok (235 km2), and Bangsal-Kedunguneng (26 km2). Six recursive digital filters (RDFs) algorithms are explored using a procedure consisting of calibration, validation, evaluation and interpretation. In this study, the period of July to September is considered as the peak of the dry season. Moreover, data for the period 1996 to 2005 is used to calibrate the algorithms. By yearly averaging, values are obtained for the parameters and then used to test performance during the validation period from 2006 to 2015. Statistical analysis, flow duration curves and hydrographs are used to evaluate and compare the performance of each algorithm. The results show that all the filters explored can be applied to estimate baseflow in the region. However, the Lyne–Hollick (with RMSE = 0.022, 0.125, 0.010 and R2 = 0.951, 0.968, 0.712) and exponentially weighted moving average or EWMA (with RMSE = 0.022, 0.124, 0.009 and R2 = 0.957, 0.968, 0.891) for the three sub-watersheds versions give the best performance.

4

Using Sentinel-2A to identify the change in dry marginal agricultural land occupation

Indarto Indarto, Putra Bayu T. W., Mandala Marga

Journal of Water and Land Development

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2020

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no. 47

89--95

EN

Dry marginal agricultural land (DryMAL) potentially use as an alternative resource for crop production. DryMAL defined as land having low natural fertility due to its intrinsic properties and forming environmental factors. This study uses Sentinel-2A imagery to map the spatial extent, compare the result of the classification, and identify the change in DryMAL occupation. The area of study (461.9 km2) is part of Situbondo Regency and is located at the eastern part of East Java, Indonesia. Sentinel-2A image captured in dry-season of 2018 use for this study. Then, supervised image classification using a maximum likelihood algorithm use for image treatment and processing. Furthermore, 450 ground control points for training areas collected during the field surveys. Five bands use in the classification process. The maps produced from the classification process were then compared to the land-use map from the year 2000. The change in DryMAL occupation from 2000 to 2018 was calculated by comparing the classified and land-use map. Supervised classification yielded an overall accuracy of 95.8% and a kappa accuracy of 93.2%. The classification produced six (6) classes of land use: (1) forest, (2) pavement or built-up area, (3) irrigated paddy field, (4) non-irrigated rural area, (5) dry marginal land and (6) water body. Globally, during the last two decades, regional development led by the Regency occupied more DryMAL area for developing plantation. The effort reduces the amount of non-irrigated and converting to the plantation, pavement areas, and irrigated paddy-field.

5

Assessment of hydrological alteration from 1996 to 2017 in Brantas watershed, East Java, Indonesia

Indarto Indarto, Andiananta Pradana Hendra, Wahyuningsih Sri, Umam Muhammad K.

Journal of Water and Land Development

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2020

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no. 46

121--130

EN

Climate, land use, and land cover change can propagate alteration to the watershed environment. The interaction between natural and human activities probably accelerates the change, a phenomenon that will generate serious environmental problems. This study aims to evaluate the change in the hydrological regime due to natural and human-induced processes. The study was conducted in Brantas watershed, Indonesia, which is the largest watershed in East Java. This area is populated by more than 8 million inhabitants and is the most urbanized area in the region. An analysis of rainfall time series use to shows the change in natural phenomena. Two land-use maps at different time intervals were used to compare the rapid development of urbanization, and the discharge from two outlets of the sub-watersheds was employed to assess hydrological changes. The indicator of hydrological alteration (IHA) method was used to perform the analysis. The daily discharge data are from 1996 to 2017. The research results show an increase in flow (monthly, 1-day, 3-day, 7-day, 30-day, and 90-day flows) in the two sub-watersheds (Ploso and Kertosono) from the pre-period (1996–2006) to the post-period (2007–2017).