ABSTRACT. LANDSLIDE IS ONE OF THE NATURAL DISASTERS THAT CAN CAUSE A LOT OF LOSS, BOTH MATERIAL AND FATALITIES. BANJARNEGARA REGENCY IS ONE OF THE REGENCIES IN CENTRAL JAVA PROVINCE WHERE LANDSLIDES OFTEN OCCUR DUE TO THE REGION'S TOPOGRAPHY AND HIGH INTENSITY RAINFALL. THEREFORE, IT IS NECESSARY TO DETERMINE THE THRESHOLD OF RAINFALL THAT CAN TRIGGER LANDSLIDES TO BE USED AS AN EARLY WARNING FOR LANDSLIDES. THE RAINFALL DATA USED FOR THE THRESHOLD IS DAILY AND HOURLY RAINFALL INTENSITY FROM REMOTE SENSING DATA THAT PROVIDES COMPLETE DATA BUT WITH RELATIVELY ROUGH RESOLUTION. SO THAT REMOTE SENSING DATA NEED TO BE RE-SAMPLED. THE REMOTE SENSING DATA USED IS CMORPH SATELLITE DATA THAT HAS BEEN RE-SAMPLED FOR DETAILING EXISTING INFORMATION OF RAINFALL DATA. THE RESAMPLING METHOD USED IS THE BILINEAR METHOD AND NEAREST NEIGHBOR BY CHOOSING BETWEEN THE TWO BASED ON THE HIGHEST CORRELATION. THRESHOLD CALCULATION USING CUMULATIVE THRESHOLD (CT) METHOD RESULTED EQUATION P₃ = 7.0354 - 1.0195P₁₅ AND INTENSITY DURATION (ID) METHOD RESULTED EQUATION I = 1.785D^-0.305. THE PEAK RAINFALL INTENSITY OCCURS AT THE THRESHOLD OF 97-120 HOURS BEFORE A LANDSLIDE OCCUR.

KEY WORDS: LANDSLIDE, THRESHOLD, RAINFALL, CMORPH

THE QUANTITY OF THE GROUNDWATER IS DEPENDENT ON THE INPUT OF THE HYDROLOGICAL CYCLE – NAMELY PRECIPITATION (RAINFALL). THE RESEARCH AREA IS IN BANTENG VILLAGE, NGAGLIK THAT LOCATED IN THE TRANSITION ZONE OF YOGYA-SLEMAN GROUNDWATER BASIN AND CATEGORIZED AS SUB-URBAN AREA. THE SEASONAL MONITORING CAN PROVIDE INFORMATION ABOUT THE RESPOND OF GROUNDWATER LEVEL IN DRY AND WET SEASONS OR EVEN ITS CONDITION IN THE CYCLONE EVENT. THE MONITORING OF GROUNDWATER LEVEL IS CARRIED OUT FOR A YEAR, FROM SEPTEMBER 2017 TO SEPTEMBER 2019 WITH THE INSTALLATION OF THE LOGGER IN 42 OBSERVATION WELLS FOR ANALYZING THE PATTERN OF GROUNDWATER LEVEL IN DRY, TRANSITION, AND WET SEASON. ANALYSIS OF LOCAL RECHARGE IN THE TRANSITION ZONE IS INTENDED TO ESTIMATE THE ROLE OF LOCAL RAINFALL ON GROUNDWATER RECHARGE USING THE WATER LEVEL FLUCTUATION (WTF) METHOD. THE REQUIRED PARAMETERS ARE THE FLUCTUATION OF GROUNDWATER LEVEL, THE TIME LAG FROM THE BOTTOM TO THE PEAK OF THE HYDROGRAPH, AND SAFE YIELD. THE RESULT IS PRESENTED BY THE HYDROGRAPH BETWEEN GROUNDWATER LEVEL – HYETOGRAPH. THE PATTERN OF GROUNDWATER FLOW IN THE THREE SEASONS IS QUITE SIMILAR, FLOWING FROM NORTH TO SOUTH WITH THE DIFFERENCE IN THE GROUNDWATER LEVEL (EQUIPOTENTIAL LINE). FLUCTUATION OF GROUNDWATER LEVEL IS POSITIVELY CORRELATED TO THE ACCUMULATION OF DAILY RAINFALL. THERE ARE FOUR SEGMENTS THAT SHOW CHARACTERISTIC OF THE GROUNDWATER LEVEL - NAMELY RECESSION (DRY), RISING LIMB FOR 56 DAYS (TRANSITION), CONSTANT FOR 100 DAYS (RAINY), AND RECESSION LIMB - AND SIX PEAKS OF THE HYDROGRAPH. THE FIRST AND SECOND SCENARIO WAS CREATED IN ORDER TO QUANTIFY THE RECHARGE OF LOCAL GROUNDWATER AT THE PEAK AND POST OF THE CEMPAKA CYCLONE. ESTIMATED LOCAL RECHARGE AT THE PEAK OF CEMPAKA CYCLONE IS 6779,88 MM/YR. ON THE OTHER HAND, ESTIMATED RECHARGE POST-CEMPAKA CYCLONE SHOWS A DIFFERENCE, NAMELY 4103,70 MM/YEAR WITHGROUNDWATER LEVEL FLUCTUATION REACHING 4,2 – 4,8 METERS.

KEYWORDS: HYDROGRAPH, GROUNDWATER LEVEL, CEMPAKA CYCLON, LOCAL RECHARGE.

RAINFALL INTENSITY IS CONSIDERED AN IMPORTANT FACTOR CONTRIBUTING TO FLOOD EVENTS WORLDWIDE. AS A CASE STUDY, THIS RESEARCH ANALYZED A SERIES OF DAILY DATA ON RAINFALLS AND FLOOD EVENTS THAT OCCURRED IN JAKARTA – INDONESIA FROM YEARS 2000-2019. THIS STUDY FOCUSED ON THE CALCULATION OF EVT (EXTREME VALUE THEORY) USING BLOCK MAXIMA WITH THE APPROACH GENERALIZED EXTREME VALUE (GEV) AND PEAKS OVER THRESHOLD APPROACH GENERALIZED PARETO DISTRIBUTION (GP). MAXIMUM LIKELIHOOD AND L-MOMENTS ARE USED FOR PARAMETER ESTIMATION. EXTREME PRECIPITATION FOR A RETURN PERIOD OF 2, 5, 10, 20, 50, AND 100 YEARS WERE OBTAINED FROM THAT CALCULATION. THE RESULT SHOWED THAT GP HAS HIGHER EXTREME RAINFALL INTENSITY THAN THE GEV RESULT. THE 2015 FLOODS EVENT HAD THE HIGHEST RETURN PERIOD (25 YEARS) WITH RAINFALL INTENSITY OF 277 MM/DAY.  THE DURATION OF THE FLOOD EVENT FOR EACH RETURN PERIODS WAS ANALYZED USING THE IDF CURVE. THIS RESEARCH CAN BE USEFUL FOR CONSIDERING THE AMOUNT OF RAINFALL INTENSITY THAT SHOULD BE ANTICIPATED FOR CITY PLANNING PARTICULARLY ON FLOOD MANAGEMENT.

DURING 12-13 JULY 2020, HEAVY RAINFALL HAD CAUSED MASAMBA, YONGKANG, AND RADA RIVERS TO OVERFLOW, CAUSING FLASH FLOODS IN THE MASAMBA REGION. THIS EXTREME EVENT RESULTED IN MANY CASUALTIES; AT LEAST 38 PEOPLE DIED AND DISPLACED THOUSANDS OF PEOPLE. THIS STUDY PRESENTS AN ANALYSIS OF THE MULTI-SCALE HYDROMETEOROLOGICAL SETTINGS THAT LED TO THE DEVELOPMENT OF THESE INTENSE STORMS IN THE MASAMBA FLOOD. BOREAL SUMMER INTRASEASONAL OSCILLATION (BSISO) NORMALIZED PC2 HAS ENTERED PHASES 4 AND 5 ON 7 - 13 JULY 2020, ASSOCIATED WITH CLOUD GROWTH IN THE INDONESIAN MARITIME CONTINENT. BESIDES, THE SUB-SEASONAL TROPICAL DISTURBANCE OF KELVIN WAVES IS CONVECTIVELY ACTIVE IN THE SULAWESI REGION ON 7 - 13 JULY, INCREASING THE PROBABILITY OF EXTREME RAIN EVENTS AT THE LOCATION. SEA SURFACE TEMPERATURES (SSTS) WERE IN WARMER CONDITIONS IN THE BONNE BAY REGION AT THE SOUTH OF MASAMBA, SUPPLYING MORE WATER VAPOR INTO THE ATMOSPHERE. THE EASTERLY WIND (AUSTRALIAN MONSOON) ENHANCED THE DIURNAL CYCLE OF THE WATER VAPOR MASS MOVEMENT FROM BONNE BAY TO THE HIGHLANDS OF MASAMBA. FROM THE OBSERVATION OF GPM SATELLITE IMAGERY, THE ACCUMULATION OF SPATIAL RAINFALL ON JULY 12 AND 13 WAS CONCENTRATED IN THE EASTERN REGION OF SULAWESI, WHICH REACHED >150 MM/DAY AND >50 MM/DAY IN MASAMBA.

HEAVY RAINS ON 24 FEBRUARY 2020 CAUSED FLOODING IN MOST OF JAKARTA AND ITS SURROUNDINGS. THE VALUE OF ONE-DAY OBSERVATION ACCUMULATED RAIN WAS RECORDED AT 277.5 MM AT THE KEMAYORAN METEOROLOGICAL STATION ON FEBRUARY 25, 2020, AT 07.00 LOCAL TIME (00.00 UTC). IN THIS STUDY, THE ANALYSIS OF EXTREME RAIN CHARACTERISTICS USING LASER PRECIPITATION MONITOR (LPM) INSTALLED AT THE KEMAYORAN METEOROLOGY STATION AND WEATHER RADAR FROM THE CENGKARENG METEOROLOGICAL STATION WITH A SPATIAL RADIUS OF 250 KM. LPM IS USED TO MEASURE THE VARIABLE DIAMETER OF THE RAINDROPS, THE SPEED OF FALLING RAINDROPS, LPM REFLECTIVITY, THE AMOUNT OF ACCUMULATED RAINFALL FOR THE TIME SERIES RESOLUTION PER MINUTE IN TXT DATA FORMAT, WHILE WEATHER RADAR IS USED TO MEASURE REFLECTIVITY SPATIALLY AND TEMPORALLY IN THE VOL DATA FORMAT. THE METHOD USED IS, FIRST, TO FIND THE RELATIONSHIP OF THE MINUTE TIME SERIES FOR LPM REFLECTIVITY WITH THE AMOUNT OF LPM RAINFALL USING A REGRESSION EQUATION. SECOND, PERFORM VARIANCE BIAS CORRECTIONS FOR THE RADAR TIME SERIES REFLECTIVITY AND THE LPM TIME SERIES REFLECTIVITY VALUES ??AT THE KEMAYORAN SITE USING R PROGRAMMING SOFTWARE. THIRD, THE RADAR REFLECTIVITY BIAS CORRECTION VALUE IS CONVERTED TO THE AMOUNT OF ACCUMULATED RAINFALL TEMPORALLY AND SPATIALLY IN JAKARTA AND ITS SURROUNDINGS. THE RESULTS OF THIS STUDY FOUND THAT THE RELATIONSHIP BETWEEN LPM REFLECTIVITY (X) AND AMOUNT OF LPM RAINFALL (Y) FORMED AN EXPONENTIAL REGRESSION RELATIONSHIP WITH THE FORMULA Y = 95178E^0.034X WITH R = 0.87. LPM CAPTURED THE PEAK OF HEAVY RAIN OCCURRING ON FEBRUARY 24 AT 18.17 UTC WITH AN INTENSITY OF 4.4 MM / MINUTE WITH A MAXIMUM DIAMETER OF 8 MILLIMETERS OF RAINDROPS WITH A MAXIMUM DROPPING SPEED OF 10 M / S. THIS IS CAUSED BY CONVECTIVE CLOUDS CONFIRMED BY RADAR'S VERTICAL CROSS-SECTION. THE ACCUMULATED VALUE OF TEMPORAL AND SPATIAL RAINFALL IN JAKARTA AND ITS SURROUNDINGS IS OBTAINED BY CALCULATING THE RADAR REFLECTIVITY VALUE AFTER BIAS CORRECTION WITH THE REFLECTIVITY OF LPM INTO THE EXPONENTIAL EQUATION. BASED ON THE RESULTS OF THE SPATIAL PLOT, IT CAN BE SEEN THAT THE DISTRIBUTION OF RAIN IN JAKARTA IS EVENLY DISTRIBUTED WITH HIGH INTENSITY WITH A TOTAL RAINFALL VALUE OF ABOVE 100 MM FOR 6 HOURS.

THE APPLICATION OF THE HYBMG PREDICTION MODEL FOR THE EAST JAVA REGION BY USING A VERIFICATION METHOD BASED ON THE PERCENTAGE ACCURACY OF THE RAINY CATEGORICAL ACCORDING TO SNI 8196: 2015. THE DATA USED IS THE HYBMG MONTHLY RAINFALL FORECAST DATA (ARIMA, ANFIS, WAVELET- FOR ARIMA AND ANFIS) LAG 1 TO 3 AND MONTHLY RAINFALL FROM 197 MAIN RAIN-POSTS IN EAST JAVA FROM AUGUST 2010 TO APRIL 2020. THE FORECASTING PROCESS IS BASED ON SIMULATION. BLANK DATA WERE FILLED USING IDW INTERPOLATION. FURTHERMORE, THE TEMPORAL ANALYSIS PROCESS IS CONDUCTED FOR NEUTRAL, EL NINO AND LA NINA. ENSO CONDITIONS IS DETERMINED USING ONI INDEX. THE RESULTS OF THE HISTOGRAM ANALYSIS SHOW THAT THE FOURTH OF HYBMG METHODS DO NOT INDICATE A SIGNIFICANT IMPROVEMENT WHEN UPDATING THE DATA, THIS JUSTIFIES THE AVERAGE OF THE 3 VERIFICATION LAGS CAN BE DONE. MEANWHILE, ARIMA VERIFICATION INCREASED TO AN AVERAGE OF 59.8% WITH THE OTHER 3 METHODS BEING LOWER THAN ARIMA AND ANFIS BEING THE MODEL WITH THE MOST UNSTABLE VERIFICATION FOR EL NINO EPISODE. GENERALLY, THE VERIFICATION OF HYBMG'S OUTPUT FOR LA NINA EPISODE IS BELOW 60% MEANWHILE FOR EL NINO EPISODE IS ONLY ARIMA WHICH CAN BE REACHED OF 60 - 70 %.

KEYWORD :HYBMG, ONI, VERIFICATION.

 

NORTH SULAWESI IS ONE OF THE PROVINCE IN NORTHERN INDONESIA THAT HAS HIGH SPATIAL ANNUAL RAINFALL VARIATIONS AND INFLUENCED BY GLOBAL CLIMATE ANOMALY THAT CAN LEAD TO EXTREME EVENTS AND DISASTER OCCURRENCE, SUCH AS FLOOD, LANDSLIDE, DROUGHT, ETC. THE PURPOSE OF THIS STUDY IS TO GENERATE HIGH RESOLUTION METEOROLOGICAL HAZARD MAP BASED ON LONG TERM HISTORICAL CONSECUTIVE DRY DAYS (CDD) OVER NORTH SULAWESI REGION. CDD WAS CALCULATED BASED ON OBSERVED DAILY PRECIPITATION DATA FROM INDONESIA AGENCY FOR METEOROLOGY, CLIMATOLOGY AND GEOPHYSICS (BMKG) SURFACE OBSERVATION STATION NETWORK (CDD_OBS) AND THE DAILY-IMPROVED CLIMATE HAZARDS GROUP INFRARED PRECIPITATION WITH STATIONS (CHIRPS) VERSION 2.0 (CDD_CHIRPS) DURING 1981 – 2010 PERIOD. THE JAPANESE 55-YEAR REANALYSIS (JRA-55) DATA OBTAINED FROM ITACS (INTERACTIVE TOOL FOR ANALYSIS OF THE CLIMATE SYSTEM) WITH SAME TIME SCALE PERIOD ALSO USED TO EXPLAIN PHYSICAL – DYNAMICAL ATMOSPHERIC PROPERTIES RELATED TO DROUGHT HAZARD OVER THIS REGION. GEOSTATISTICAL APPROACH USING REGRESSION KRIGING METHOD WAS APPLIED AS SPATIAL INTERPOLATION TECHNIQUE TO GENERATE HIGH RESOLUTION GRIDDED (0.05^O X 0.05^O) DROUGHT HAZARD MAP. THIS METHOD COMBINES A REGRESSION OF CDD_OBS AS DEPENDENT VARIABLE (TARGET VARIABLE) ON CDD_CHIRPS AS PREDICTORS WITH KRIGING OF THE PREDICTION RESIDUALS. THE RESULTS SHOW THAT MOST OF THE AREAS WERE CATEGORIZED AS MEDIUM DROUGHT HAZARD LEVEL WITH CDD VALUES RANGING FROM 80-100 DAYS. MEANWHILE, SMALL ISLANDS AROUND MAIN SULAWESI ISLAND SUCH AS SANGIHE AND KARAKELONG ISLAND ARE DOMINATED BY LOW DROUGHT HAZARD LEVELS WITH CDD VALUES RANGING FROM 50-60 DAYS. HIGHEST LEVELS OF DROUGHT HAZARD AREA ARE LOCATED IN SOUTH BOLAANG MONGONDOW REGENCY.

 

: CDD, DROUGHT HAZARD, EXTREME CLIMATE, GEOSTATISTICS, DAILY-IMPROVED CHIRPS

 

A SUMATRA SQUALL IS A LINE OF CONVECTIVE CLOUD USUALLY DEVELOPS AT NIGHT OVER SUMATRA OR THE MALACCA STRAITS. THIS NOCTURNAL SQUALL CAUSES BAD WEATHER IN THE REGION IT CROSSES. STUDIES RELATED TO THE SUMATRAN SQUALL ARE NEEDED TO INCREASE AWARENESS OF THE DISASTERS THEY CAUSE. SATELLITES ARE ONE OF THE MOST EFFECTIVE METHODS FOR OBSERVING CLOUD GROWTH AND MOVEMENT. RGB COMPOSITES OF SATELLITE IMAGERY CAN GIVE COMPLETE / COMPOSITES INFORMATION FROM MANY WAVELENGTH CHANNELS OF THE SATELLITE. ONE OF THE LIMITATIONS OF RGB COMPOSITES IMAGERY IS NOT ALL OF THE RGB PRODUCTS CAN BE USED FOR BOTH DAYTIME AND NIGHT TIME. THIS STUDY WAS CONDUCTED TO DETERMINE THE ACCURACY OF USING THE RGB PRODUCT MODALITY FOR DETECTING THE SUMATRAN SQUALL AT NIGHT. THE DATA USED ARE HIMAWARI-8 AND GSMAP SATELLITE DATA FOR 2020. MODIFIED RGB PRODUCTS CAN SHOW AREAS OF SEVERE WEATHER CLOUDS CLEARLY AND SIMILARLY TO HCAI CLOUD TYPE IMAGES. SATELLITE IMAGERY CAN SHOW SUMATRA SQUALL'S DEVELOPMENT AND ITS MOVEMENT EASTWARD TOWARDS PENINSULAR MALAYSIA IN THE EARLY HOURS OF THE MORNING.

ABSTRACT - MESOSCALE CONVECTIVE COMPLEX (MCC) WAS FORMED ON THE INDIAN OCEAN, WEST OF SUMATRA ISLAND ON MAY 19^TH, 2020, BASED ON THE IMAGE RESULTS BAND INFRARED (IR) SHOWING THAT THE EXISTING MCC GREW WITH A MAXIMUM AREA OF ??THE CORE AND CLOUD COVER, RESPECTIVELY 483,338 KM² AND 1,367,690 KM², WITH DURATION FOR 8 HOURS. THE MCC PHENOMENA CAUSED BAD WEATHER AND PROLONGED RAIN INTENSITY ON SUMETERA ISLAND, ESPECIALLY LUBUKLINGGAU CITY, WHICH EXPERIENCED FLASH FLOODS DUE TO RAIN WITH INTENSITIES REACHING 31.6 MM / HOUR. THIS PAPER AIMS TO DETERMINE THE GROWTH CHARACTERISTICS OF MCC, ATMOSPHERIC CONDITIONS AND RAINFALL IN LUBUKLINGAU. THROUGH THE INTERPRETATION OF SATELLITE IMAGERY DATA, THE RGB TECHNIQUE DAY CONVECTIVE STORM CLOUDS SEEN THEIR COLLECTION WITH A REDDISH YELLOW CLOUD TOP TEMPERATURE REACHED -78^OC. ANALYSIS CONDITIONS WERE ALSO CONDUCTED ON THE PARAMETERS OF WIND, SEA SURFACE TEMPERATURE, SYNOPTIC OBSERVATION DATA, AND THE DATA PHENOMENON HIDROMETEROLOGI OTHERS FROM BUREU OF METEOROLOGY (BOM), THE METEOROLOGY, CLIMATOLOGY AND GEOPHYSICS AGENCY (BMKG) AND THE NATIONAL OCEANIC AND ATMOSPHERIC (NOAA). BASED ON THE DESCRIPTIVE ANALYSIS, SHEAR OCCURRED IN THE SUMATRA REGION FOLLOWED BY THE OCCURRENCE OF SEA SURFACE TEMPERATURE ANOMALIES IN THE INDIAN OCEAN WATERS OF 2^OC - 3^OC, FOLLOWED BY THE ACTIVATION OF MJO IN PHASE III WHICH SUPPORTED THE FORMATION OF CUMULONIMBUS (CB) CLOUDS IN THE INDIAN OCEAN.

KEYWORDS: MCC, HIMAWARI-8 SATELLITE, RGB

HEAVY RAIN HIT SEVERAL PARTS OF INDONESIA ON 14^TH DECEMBER 2020, INCLUDING WEST NUSA TENGGARA PROVINCE. INFORMATION ABOUT THE DISTRIBUTION OF CONVECTIVE CLOUDS IS NEEDED IN ANALYZING THE EXTREME RAIN THAT OCCURS. THIS RESEARCH USED THE CLOUD CONVECTIVE OVERLAYS (CCO) METHOD IN THE GRADS APPLICATION, RED GREEN BLUE CONVECTIVE STORMS (RGB-CS) AND SPLIT WINDOWS ALGORITHM IN THE SATAID APPLICATION. DATA ARE COLLECTED WITH FORMAT .Z AND .NC RESOLUTION OF HIMAWARI-8 SATELLITE. WARM SEA SURFACE TEMPERATURES, THE PRESENCE OF ACTIVE LA NINA AND MJO IN THE QUADRANT 5 ALSO AFFECTS THE POTENTIAL FOR CONVECTIVE CLOUD GROWTH IN THE AREA. SATELLITE IMAGERY SHOWS THAT HEAVY RAIN IN THE AREA IS CAUSED BY CUMULONIMBUS (CB) CLOUD ACTIVITY WITH CLOUD TOP TEMPERATURES REACHING -48 ° C TO -80 ° C. HOWEVER, THE CCO METHOD, RGB-CS OR THE SPLIT WINDOW ALGORITHM, CAN CAPTURE CLOUD DISTRIBUTION AND SHOW ALMOST THE SAME CONVECTIVE CLOUD RESULTS.

KEYWORDS: CCO, EXTREME RAIN, HIMAWARI-8 SATELLITE, RGB, SWA

INDONESIA WAS SHOCKED AGAIN WITH A TORNADO INCIDENT ON NOVEMBER 22, 2018 IN THE JAKARTA AREA. THIS INCIDENT CAUSED MANY LOSSES. IN THIS REGARD, A STUDY WAS CONDUCTED TO DETERMINE THE HOOK ECHO AND BOW ECHO PATTERNS OBSERVED IN REFLECTIVITY PRODUCTS AND MESOCYCLONE PATTERNS IN VELOCITY PRODUCTS AS CHARACTERISTICS OF TORNADO. THE STUDY USED THE CENGKARENG GEMATRONIC RAW DATA RADAR THAT WAS PROCESSED TO PRODUCE CMAX, VCUT, AND CAPPI (V) AT 0,5 KM,1,0 KM AND 1,5 KM HEIGHTS OVERLAYED BY HWIND. IN ADDITION, THE ANALYSIS WAS ALSO CARRIED OUT USING HIMAWARI-8 SATELLITE IMAGE DATA USING SATAID (SATELLITE ANIMATION AND INTERACTIVE DIAGNOSIS) AS A SUPPORT FOR THE RESULTS OF RADAR ANALYSIS. FROM THE ANALYSIS THAT HAS BEEN DONE, IT IS KNOWN FROM THE WEATHER RADAR THAT TORNADO IN JAKARTA IS DOMINANT OF 15.00 WIB. THE GROWTH OF CYCLONE-PRODUCING CLOUDS OCCURS VERY QUICKLY WITH A REFLECTIVITY VALUE BETWEEN 35 - 45 DBZ AND WIND SPEED UP TO 35 KNOTS. ANALYSIS OF SATELLITE IMAGERY SHOWS A SIGNIFICANT DECREASE IN CLOUD PEAK TEMPERATURE SO THAT THE FORMATION OF CONVECTIVE CLOUDS IN THE FORM OF CUMULONIMBUS CLOUDS INDICATES THE PHENOMENON OF TORNADO.

THE FLOOD THAT OCCURRED IN THE KALUKKU AREA, WEST SULAWESI ON OCTOBER 15 2020 RESULTED IN THE INUNDATION OF SEVERAL SHOP AND HOUSES. THE PURPOSE OF THIS RESEARCH IS TO ANALYZE THE METEOROLOGICAL FACTORS THAT INFLUENCE THIS EVENT. THE METHOD USED IS TO ANALYZE DATA ON HIMAWARI 8-EH SATELLITE IMAGERY, STREAMLINE, AND AIR LABILITY INDEX FOR THE LOCAL SCALE, ANALYSIS OF ENSO, IOD, SOI, AND MJO DATA FOR A GLOBAL SCALE, AND ANALYSIS OF SEA SURFACE TEMPERATURE (SST) AND ANOMALIES AND HUMIDITY AIR FOR A REGIONAL SCALE. BASED ON THIS ANALYSIS, IT CAN BE CONCLUDED THAT WHAT CAUSES CONVECTIVE CLOUD GROWTH IS THE PRESENCE OF CONVERGENCE, WARM SST, ACTIVE MJO IN QUADRANT 5, WET HUMIDITY IN LAYERS 850 MB AND 700 MB, AND LARGE CAPE VALUES.

 

 

THE LOCATION OF PELALAWAN WHICH CROSSES THE EQUATOR CAUSES THE AREA TO GENERALLY RECEIVE MAXIMUM SUNSHINE EVERY DAY SO THAT THE AIR TENDS TO BE WARM WHICH CAUSES THE POTENTIAL FOR HAIL OCCURENCE IN PELALAWAN IS SMALL. ON SEPTEMBER 23, 2019 THERE WAS HAIL IN DESA PULAU, PELALAWAN REGENCY, RIAU PROVINCE, WHERE THIS HAIL WAS THE FIRST AND UNIQUE BECAUSE IT WAS OCCURRED WHEN THE ENTIRE RIAU AREA WAS FILLED WITH SMOG DUE TO FOREST AND LAND FIRES. HAIL THAT OCCURRED IN PULAU MUDA VILLAGE, PELALAWAN WAS NOT ACCOMPANIED BY EXTREME RAIN AND DID NOT CAUSE MATERIAL HARM TO THE POPULATION. HOWEVER, A STUDY OF ATMOSPHERIC CONDITIONS BEFORE, DURING AND AFTER THE HAIL OCCURRED TO BE USED AS A REFERENCE FOR EARLY WARNING OF FUTURE EVENTS. PREVIOUSLY, RESEARCH ON THE ANALYSIS OF HAIL EVENTS IN SEVERAL REGIONS OF INDONESIA HAD BEEN CARRIED OUT. THIS RESEARCH WAS CONDUCTED TO STUDY ATMOSPHERIC CONDITIONS IN THE RIAU AREA IN THE OCCURENCE OF HAIL WHICH CAN BE USED AS A REFERENCE IF THERE WILL BE SIMILAR OCCURENCE IN THE FUTURE. THE RESEARCH WAS CONDUCTED WITH DESCRIPTIVE ANALYSIS OF ATMOSPHERIC CONDITIONS USING SURFACE WEATHER DATA, HIMAWARI-8 RGB IMAGES, CLOUD TOP TEMPERATURE, AND VERTICAL VELOCITY PROFILE. BASED ON THE ANALYSIS, THERE WAS A CHANGE IN SURFACE WEATHER PARAMETERS COMPARED TO THE WEATHER ON THE DAY BEFORE AND AFTER THE HAIL EVENT. THE OCCURRENCE OF HAIL IS CAUSED BY CUMULUNIMBUS CLOUDS WITH A LARGE CONTENT OF WATER VAPOR, LARGE ICE PARTICLES AND STRONG UPDRAFT ALONG WITH DOWDRAFT.

PROBABLE MAXIMUM FLOOD (PMF) IS USED TO ENSURE MAXIMUM SAFETY AND RELIABILITY IN THE DESIGN OF HYDRAULIC STRUCTURES SUCH AS RESERVOIRS AND DAMS. THE PMF VALUE CAN BE OBTAINED THROUGH THE PROBABLE MAXIMUM PRECIPITATION (PMP) VALUE, WHICH IS THE MAXIMUM RAINFALL THAT MAY OCCUR IN AN AREA WITHIN A CERTAIN PERIOD OF TIME. THE PURPOSE OF THIS STUDY WAS TO ESTIMATE THE VALUE OF PMP AND PMF IN THE UPPER CITARUM WATERSHED AND TO DETERMINE THE EFFECT OF SPATIAL DIFFERENCES AND PMP DURATION ON PMF DISCHARGE THROUGH THE APPLICATION OF TWO SCENARIOS.

 

PMP IS OBTAINED BY USING GLOBAL SATELLITE MAPPING OF PRECIPITATION (GSMAP) RAINFALL DATA WHICH HAS A TEMPORAL RESOLUTION OF 1 HOUR. THE RAINFALL DATA USED ARE CORRECTED FIRST WITH BIAS CORRECTION AND THE BIAS CORRECTION RESULTS ARE ABLE TO CHANGE THE DISTRIBUTION OF THE GSMAP RAINFALL DATA CLOSER TO THE OBSERVATION DATA. FURTHERMORE, THE PMP VALUE WILL BE OBTAINED USING THE HERSHFIELD STATISTICAL METHOD, AND THE PMF VALUE IS OBTAINED USING THE PMP AS AN INPUT VALUE IN THE GRIDDED SURFACE SUBSURFACE HYDROLOGIC ANALYSIS (GSSHA) HYDROLOGICAL MODEL.

 

SPATIALLY, THE LARGEST PMP VALUES ??WERE IN THE CIMAHI AND SOREANG AREAS REACHING 100-150 MM WITH A DURATION OF 6 TO 12 HOURS, CIMAHI AND BANDUNG REACHING 250 MM FOR A DURATION OF 24 HOURS. THE SIMULATION OF THE GSSHA MODEL WITH SCENARIO A IS THE PMP VALUE OBTAINED FROM EACH GRID DATA AND SCENARIO B IS THE PMP VALUE OBTAINED THROUGH RAINFALL IN THE UPPER CITARUM WATERSHED. THE RESPONSE OF THE UPPER CITARUM WATERSHED, WHICH SHOWS SIMILARITIES TO THE TWO SCENARIOS, SHOWS THAT SCENARIOS A AND B CAN BE USED TO CALCULATE PMF DISCHARGE WITH A PMP DURATION OF MORE THAN OR EQUAL TO 72 HOURS. SCENARIO A PRODUCES 13.12% HIGHER PMF DISCHARGE THAN SCENARIO B. THE SIMILARITIES AND DIFFERENCES ARE INFLUENCED BY THE INTENSITY OF PMP AND THE CONCENTRATION TIME OF THE UPPER CITARUM WATERSHED.

KEYWORDS: GSMAP, BIAS CORRECTION, PMP, PMF, WATERSHED RESPONSE, CONCENTRATION TIME.