Landslides are one of the most disastrous natural hazards that frequently occur in Indonesia. In 2017, Balai Sabo developed an Indonesia Landslide Early Warning System (ILEWS) by utilizing a single rainfall threshold for an entire nation, leading to inaccuracy in landslide predictions. The study aimed to improve the accuracy of the system by updating the rainfall threshold. We analyzed 420 landslide events in Java with the 1-day and 3-day effective antecedent rainfall for each landslide event. Rainfall data were obtained from the Global Precipitation Measurement (GPM), which is also used in the ILEWS. We propose four methods to derive the thresholds: the first is the existing threshold applied in the Balai Sabo ILEWS, the second and third use the average and minimum values of rainfall that trigger landslides, respectively, and the fourth uses the minimum value of rainfall that induces major landslides. We used receiver operating characteristic (ROC) analysis to evaluate the predictability of the rainfall thresholds. The fourth method showed the best results compared with the others, and this method provided a good prediction of landslide events with a low error value. The chosen threshold was then applied in the Balai Sabo-ILEWS.
The Paris Agreement, signed in 2015, is intended to limit global warming well below 2°C. This paper is aimed to assess the potential key impact of 2°C and 4°C global warming on the characteristics of precipitation extremes over Indonesia. For this purpose, the CSIRO-Mk3.6.0 global projections forced by the representative concentration pathway (RCP8.5) scenario is dynamically downscaled using the RegCM modelling system. The results show that under these two global warming level, total annual precipitation (PRCPTOT) will decrease in most regions. Consistently, the dry spell duration (CDD, consecutive dry days) is projected to increase. On the other hand, the frequency and the intensity of precipitation extremes (R50mm and RX1day) are projected with mix increase and decrease tendency. Seasonally, the contrast changing of PRCPTOT is projected. PRCPTOT tends to decrease during dry season (June-July-August, JJA) and tends to increase during wet season (December-January-February, DJF). The similar pattern is found for other indices e.g. CDD, R50mm and RX1day. In general, changes at 4°C global warming are statistically more significant and more intensified compared to that at 2°C. Our findings suggest the benefit of limiting global warming at a lower level.
To determine the level of light pollution due to human activities, we performed sky-brightness measurements at Bosscha Observatory, Indonesia (107°36′E; 6°49′S, 1300 m above sea level) for seven years from 2011 to 2018, using a portable photometer pointed at the zenith. From 1692 nightly records, we found that the average brightness on moonless nights reached the 19.70 ± 0.84 and 19.01 ± 0.88 astronomical magnitudes per square arcsecond (mpass), with median values of 19.73 mpass and 19.03 mpass for the AM and PM periods, respectively. The darkest skies occurred in the peak of the summer season during the month of July, which corresponds to the lowest annual temperature, precipitation, and relative humidity. The internal temperature of our Sky Quality Meter is adequately stable, and our results correlate well with other measurements. The sky brightness depends on the age of the Moon (days past new Moon) and on seasonal monthly variations, but it is not related to the lunar distance. The night-SB quality can be modified by the coupled climate system as a diurnal cycle to an 11-year solar cycle. The cities around the Observatory, Bandung and Lembang, clearly make strong contributions to light pollution in the area due to unshielded light sources.
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