Lahar Flow Research Articles

Dynamics of rain-triggered lahars and destructive power inferred from seismo-acoustic arrays and time-lapse camera correlation at Volcán de Fuego, Guatemala

AbstractLahars, or volcanic mudflows, are one of the most devastating natural, volcanic hazards. Deadly lahars, such as the one that occurred after the Nevado del Ruiz, Columbia eruption in 1985, in which at least 23,000 people tragically lost their lives, threaten the safety and well-being of humans, the economy, and the infrastructure of many of the communities living in the vicinity of volcanoes. Due to their complex flow behaviors, lahars remain a major challenge to those studying them. We present an analysis of several rain-triggered lahar events at Volcán Fuego in Guatemala using both seismic and infrasound monitoring to quantify both ground vibrations and low-frequency atmospheric sound waves associated with these mudflows. Geophysical data collected over this field campaign quantifies flow parameters such as velocities, stage and the frequency of these rain-triggered lahars. Time-lapse imagery of lahar flows is compared with filtered seismo-acoustic signal characteristics to ascertain stage predictions and relationship to stage fluxes. Using random forest regression models, we establish moderate correlations (correlation coefficient modes 0.48–0.53) with statistical significance (p value = 0.01–0.02) between signal energetics and respective stage. Compiling a catalog of rain-triggered lahar events in Volcán de Fuego’s drainages over a season permits a dataset amenable to statistical analysis. Our goal is the development of new-generation geophysical monitoring tools that will be capable of remote and real-time estimation of flow parameters.

Ancient Disaster, the Cause of the Burial of the Kumitir Archeological Site

The Kumitir site, associated with the Majapahit Empire, is a significant archeological discovery. Archeologists from the East Java Cultural Heritage Preservation Center (BPCB), uncovered a structure at this site, buried beneath boulder-sized rocks. According to historical literature, the collapse of Majapahit was caused by volcanic eruptions from the Anjasmoro, Arjuno, or Welirang complexes. Therefore, this study aimed to recreate the gravity-driven mass flow covering the Kumitir Site. Geological surveys, including sediment structure analysis and grain orientation measurements, were conducted to provide new information on paleocurrent and ancient sedimentary processes at the site. Digital Elevation Map (DEM) and the Laharz simulation tool facilitated the creation of reconstructed lahar flow maps using open-source DEM data with an eight-meter resolution. The results of the boulder analysis showed that a paleochannel played a significant role in the burial site, with two sources identified, namely Mount Welirang (Welirang alluvial fan) and the Anjasmoro complex (Old Jatirejo alluvial fan). Meanwhile, the combination of methods applied signified the direction of the Welirang alluvial fan (ESE-NNW) and the Jatirejo Tua alluvial fan (SSW-NNE). Volumes of 9 million m3 and 65 million m3 were the most relevant parameters for estimating the lahar flows of the western and eastern craters, respectively.

Simulation of lahar flow potensial hazards in seulawah agam volcano eruption-aceh

Abstract Seulawah Agam volcano is an active stratovolcanic volcano located on Sumatra Island. During the decade following the phreatic eruption in 1839 up to now, there have only been a few small-scale increases in activity. The hazards associated with volcanic eruptions can be divided into primary hazards and secondary hazards. One type of significant secondary hazard is lahar flow. The consequences of this volcanic eruption must be overcome because the impact is the same as the main hazard, especially if efforts to overcome it are not taken seriously. Therefore, simulations are needed to understand the lahar flow patterns that can occur due to the eruption of the Seulawah Agam volcano. This lahar flow simulation is based on Digital Elevation Model (DEM) data, namely DEMNAS, and uses the LAHARZ application, which is based on Geographic Information Systems (GIS). The LAHARZ software is designed to calculate potential hazard zones exposed to lahar flows based on volume parameters. Lahar flow simulations were made in hydrological channels with several lahar volume scenarios, such as 1 x 105 m3, 1 x 106 m3, and 5 x 106 m3. The lahar volume estimate used is based on information from historical data on volcanic eruptions whose characteristics are almost the same as the Seulawah Agam volcano. This volume scenario shows differences in the extent of lahar flows and the size of the affected area. The results of this lahar flow simulation can be one of the first steps in efforts to mitigate the hazards of volcanic eruptions in the future.

Lahar flow characteristic of Semeru Volcano based on Flow-R Model and its countermeasure

Lahar flows represent a consequential outcome of volcanic eruptions, posing a natural hazard with the potential to profoundly impact both society and infrastructure. These fast-moving streams of volcanic lahar surge from elevated terrains to lower altitudes, commonly referred to as lahar flows. The Rejali Watershed, nestled in Lumajang Regency, East Java, Indonesia, serves as one of the key watersheds sourced from the elevated slopes of the Semeru Volcano, eventually merging into the Indian Ocean as its outlet. The primary objective of the study is to uncover the distinct characteristics of Semeru Volcano’s lahar flows and suggest feasible countermeasures aimed at averting potential future disasters. A thorough comprehension of the potential dangers associated with lahar flows is imperative in identifying the requisite countermeasures and regulations to be implemented for the purpose of disaster risk reduction. The findings highlight the utility of the model in effectively mapping the impact of the Semeru volcanic eruption. This is achieved through the utilization of back analysis to acquire insights into the characteristics of these lahar-related disasters. While the model exhibits a good correlation with reality, as evidenced by the Sentinel 2 image, it falls short of adequately representing certain specific areas.

An early Miocene (Aquitanian) mangrove fossil forest buried by a volcanic lahar at Barro Colorado Island, Panama

We describe remains on an Early Miocene mangrove forest, based on a fossil wood assemblage, discovered on Barro Colorado Island, Panama. Sedimentological and stratigraphic analysis suggests that the fossil trees grew in marginal marine to coastal fluvial settings and were buried under a volcanic lahar flow in a single event. Radiometric analyses of a tuff associated with the fossils gives a date of ∼22.79 Ma indicating an assignment to the Aquitanian stage of Early Miocene. At this time, central Panama was part of a long and narrow peninsula with intense volcanic activity that connected it with North America and was separated from South America by the Central American Seaway. A total of 121 fossil wood specimens were located. Wood anatomy indicates that most of the identifiable specimens belonged to the same morphotype, which has anatomical traits similar to Sonneratia (Lythraceae), a mangrove tree that is native to Southeast Asia. We named this morphotype as a new fossil species: Sonneratioxylon barrocoloradoensis Pérez-Lara., sp. nov. Biomechanical estimates indicate that S. barrocoloradoensis had a mean tree height of 25 m with some specimens reaching 40 m, in contrast to modern Sonneratia and other extant mangrove forests, which generally have lower mean heights. The dominance of S. barrocoloradoensis, its similarity to Sonneratia, and the depositional setting suggest that the fossil wood assemblage on Barro Colorado Island comprised a mangrove forest growing along the coast of the volcanic chain of central Panama.

Lahar Inundation Estimation of Mount Semeru Relating to the 4th December 2021 Volcano Eruption

The Semeru volcano – located at the boundary region of Lumajang and Malang districts of East Java province, Indonesia – which is categorized as one of the active volcanoes in Indonesia was enormously erupted the volcanic materials – the hot lahar and the volcanic ash - on 4th December 2021. The scale of the eruption event caused some disaster to several villages along the path of the lahar and volcanic ash in south to southeast direction from the Mount Semeru lahar dome. An inundation simulation of the lahar is done as a contribution to mitigating the disaster that may potentially occur in the future. The LAHARZ algorithm was used for these estimation calculations. The Digital Terrain Model (DTM) and Digital Surface Model (DSM) were used as the base data for estimating and simulating the lahar inundation scenario. The use of two types of elevation model data in the simulation was done for study the inundation characteristics in the presence of forest vegetation. Three scenarios of lahar volume were used for simulating the inundation over elevation models. Results of the estimation then be compared to the actual lahar inundation that was delineated from the high-resolution satellite images. Lahar flow simulations using DTM show that more flows were formed compared to using DSM. The DTM simulation results showed a flow that more closely resembled the existing flow map compared to the DSM simulation results.

The long-term impact of humanitarian housing interventions following the 2010 Merapi eruption

There is strong evidence of the short-term impact of humanitarian interventions after disasters, however, relatively less is known about what, if any, impact this support has on long-term recovery outcomes in communities. This research examined long-term housing outcomes following assistance provided after the 2010 Merapi eruption in Yogyakarta, Indonesia. We surveyed 316 households who received and did not receive housing assistance following damaging lahar flows in the community of Jogoyudan to assess housing quality through a multi-dimensional measure. Ordinary Least Squares (OLS) regression was used to evaluate the relationship of humanitarian assistance on housing quality outcomes, controlling for respondent and household demographics as well as the impacts of the disaster. Findings indicate that post-disaster housing assistance was positively correlated with higher long-term housing quality. Land tenure was found to be the strongest predictor of housing quality, explaining nearly a fifth of variance in housing quality. Livelihoods and construction abilities were also found to be significant predictors of long-term housing quality. Our results demonstrate the value of post-disaster housing programs in raising the living standard of recovering communities and the institutional, economic, and knowledge systems that support housing markets.

Taking the advantage of Participatory Geographic Information System (P-GIS) in validating Semeru disaster prone area map in Oro-Oro Ombo, Lumajang

Desa Oro-Oro Ombo is located on the south-eastern flank of Semeru Volcano. It sits in a disaster-prone area (KRB) level I, II, and III due to the high possibility of being impacted by volcanic ash fall and lahar flow. However, the 1996 KRB map is no longer relevant because the impact of the 2021 Semeru eruption expanded more than expected. As a result, it increased the hazard and vulnerability of the village in the future. Therefore, it is crucial to generate the post-2021 KRB map and study the community’s perspective and knowledge about it. This research adopted a qualitative approach for data-gathering, i.e., in-depth interviews with key informants and the P-GIS methods. Interviews were conducted with the representative of BPBD Lumajang, coordinator of Semeru observatory station, coordinator of lahar flow observatory station, representative of local government, and impacted inhabitants. Meanwhile, P-GIS was applied to validate the KRB map. The study found a difference in the KRB coverage due to the deviation of the village administration boundaries. This research then produced a validated post-2021 Semeru eruption KRB map that can be utilized as the basis for further volcanic disaster risk management of Oro-Oro Ombo. According to the result the current map is going to reform the knowledge towards the recent hazards and risks.

Mapping the Semeru lahar-flood hazard of Supiturang Village using the analytical hierarchy process (AHP) method

Supiturang is one of the villages in Kecamatan Pronojiwo, Kabupaten Lumajang that sits on the lahar flow path of Semeru Volcano. The village constantly faces a lahar-flood hazard, inevitably impacting the local community. Therefore, this paper aims to map the lahar-flood hazard of Supiturang village using the analytical hierarchy process (AHP) method. The main parameters are 1) slope (%), 2) distance from drainage (m), 3) elevation (m ASL), 4) rainfall (mm), and 5) land cover (water body/bare land/forest/grassland/plantation/ricefield/mixed agriculture/built-up area). This research is a descriptive-quantitative study that used survey and geographic information system (GIS) approaches. The result showed that the lahar-flood hazard class of Supiturang varies from very low, low, moderate, high, to very high. The very high hazard class is distributed near the lahar flow path. Despite most settlements being in the moderate hazard class, some are in the high and very high hazard class. The findings from this research can advantage the further improvement and development of evacuation routes, assembly points, refuges, observatory stations, and other related Semeru Volcano disaster risk mitigation actions.

Geomorphological mapping and landform characterization of Semeru volcano after the eruption in 2021

The eruption of the Semeru volcano in 2021 has diverse impacts on the landscape and surroundings. It is essential to detect recent landscape features to promptly evacuate personnel and property near the volcano and take emergency treatment measures in case of sudden danger. This study presents a detailed geomorphological map on a 1:50.000 scale for the Semeru volcano after the eruption in 2021. The analysis of the hybrid approach and the on-screen image interpretation (OSII) method on DEM data, optical satellites, and lithology units was carried out to obtain morphological, morphochronological, and morphoarrangement information. While, morphoprocess information was obtained through field observations. We used DAS Rejali for our study area. The results of identifying geomorphological conditions divide the Rejali watershed area into 32 landforms consisting of landform units from volcanic, structural, fluvial, and marine processes. Twenty-three land units in the research location are landforms from volcanic processes. This condition causes morphological conditions, material availability, and processes that dominantly reflect the characteristics of an active volcano. In addition, the landform units from the fluvial process in the Rejali watershed area were identified as many as six units in the form of floodplains of lahar flows along the main river. Landforms with structural genesis were placed in Mandalika formation and diorite rock breakthrough. The structural formation in the Rejali watershed has retention and rock structures that are not easily eroded by water. It becomes a bottleneck formation as a barrier between the upstream and middle areas

Hazards Mitigation of Lahar Flows on Semeru Volcano after the 4 December 2021 Eruption Based on PS-InSAR

Volcanic eruption is one of the phenomena that can change the volcanic landscape drastically. Monitoring of volcanic edifices after eruptions should be considered to further understand the potential hazards in the future. Satellite monitoring is a reliable technique for assessing deformation in a volcano. InSAR was applied to detect material build-up after the eruption phase of Semeru Volcano in December 2022. As a consequence of the opening crater along with the InSAR result, a lahar product after the eruption was deposited in the southwest direction. Significant deformations were indicated by PS-InSAR near the crater, which was characterized by a LOS displacement of -10 to -40 mm/year, indicating scouring of the pyroclastic material moving down the slope. The accumulation of pyroclastic flows from the abrading process below was detected in the proximal zone of Semeru, as shown by the positive LOS displacement ranging from 10 to 40 mm/year. The field survey conforms to the PS InSAR results, where unconsolidated material, ranging in size from gravel to boulders, piles up approximately 4-5 m in Curah Kobokan. Highly unconsolidated material tends to move easily by water and threaten the surrounding settlements. Overlying PS InSAR and drainage pattern in the flank of Semeru, concluding several locations that have a high-risk potential of being affected by lahar flows are Curah Kobokan, Supiturang Village, Pronojiwo District, then Tulungrejo, Pasropan Village, Pasrujambe District, Lumajang Regency.

Determination of potential secondary lahar hazard areas based on pre-and post-eruption UAV DEMs: Automatic identification of initial lahar starting points and supplied lahar volume

• Lahar starts point (LSP) and supplied volume (SLV) constrain inundation prediction. • Uncertainty of LSP and SLV parameters are subjected to misinterpreted prediction. • Proposed PEARPY program aims to estimate actual values of the parameters. • The program produces a realistic lahar simulation with a satisfactory similarity. • High-detailed UAV DEM prevents over or underestimation of lahar run-out prediction. Secondary lahars, generated after volcanic eruptions, may pose significant threats to life and infrastructure. Secondary lahars typically develop from ash deposits and other volcanic debris that remobilize downstream via intense rainfall. The lahar inundation zone after eruptions must be predicted to minimize the impact. This prediction can be modeled based on digital elevation models (DEMs) and two parameters associated with lahar simulations: the lahar starting point (LSP), which indicates the potential locations at which a lahar flow may initiate, and supplied lahar volume (SLV), which is the lahar volume corresponding to each LSP. These parameters are typically determined by assumptions based on past lahar events, which may be unrealistic and often misinterpreted in the inundation prediction. To address this problem, this paper proposes an automated method to estimate the LSP and SLV based on pre-and post-eruption DEMs generated by unmanned aerial vehicle (UAV) images and simulate the inundation zone using the LAHARZ model. The study site is located in the southeast region of Mount Agung (Indonesia), and the objective is to mitigate the potential secondary lahar hazard after the 2017–2019 eruption crisis. Results show that the parameter estimations using the high-resolution UAV DEM and LAHARZ produce a realistic lahar simulation, with a satisfactory similarity of 82%, as verified against the lahar footprint. Moreover, we compare the results with those obtained using TerraSAR-X DEM and demonstrate the importance of using a detailed UAV DEM to avoid underestimating the lahar runout and ensure that the simulated inundation zones mimic real lahars.

Detection of Lahar Flow Direction from Semeru Eruption on 4 December 2021 using Gravity Method

Detection of Lahar Flow Direction from Semeru Eruption on 4 December 2021 using Gravity Method

Detailed Cartography of Cotopaxi’s 1877 Primary Lahar Deposits Obtained by Drone-Imagery and Field Surveys in the Proximal Northern Drainage

Cotopaxi is an active volcano in Ecuador, whose eruptions are characterized by producing destructive primary lahars which represent a major risk for the country. The hazard assessment related to such lahars relies largely on the knowledge of the latest event, which occurred on 26 June 1877, for either scenario definition or simulation calibration. A detailed (1:5000 scale) cartography of the deposits belonging to that eruption has been obtained in the proximal northern drainage of Cotopaxi. The cartography was performed through a combination of geological fieldwork, as well as the analysis and interpretation of high-definition imagery obtained by drone surveys combined with the Structure from Motion technology for image processing. Such imagery included red and green visible bands, and a near-infrared band, which allowed the obtention of NDVI imagery where the primary lahar deposits were identified and cartographed with support of fieldwork data. Both data sources are mutually complementary, and the final cartography would be impossible if any of them were not available. The results obtained represent a significant advance for the level of detail with respect to previous cartographic works. Moreover, they should allow an improved calibration of the new generation of numerical models that simulate lahar flow for hazard assessment at Cotopaxi.

The Lahars of the South-East slope of Mount Cameroon: geological study, economic interest and impacts of their exploitation on the environment

Mount Cameroon is the site of explosive eruptions with the emission of ash, slag and lava flows. Mudflows, known as Lahars, can also be observed. These Lahars are mainly found in the lower part of the south-eastern slope. The outcrops observed on this flank show that these Lahars are very extensive and are avalanches of volcanic material, which flowed down the slopes of the volcano after the eruptions. The different outcrops observed are separated by pyroclastic products on which the lahars rest. The components of these lahars are generally black or grey basalts. The main granulometric characteristic of the deposits of these lahars is their heterometry. The size of the material varies from a few meters to the clay fraction. Large concentrations of mineable material are found in the watercourses. These materials are exploited in order to produce aggregates for civil engineering. This exploitation has consequences on the immediate environment. In addition to climatic factors, several parameters have influenced the mobilities and emplacement of the lahars on the south-eastern slope of Mount Cameroon: the slope, the volume and thickness of the deposits, the nature and physico-hydric characteristics of the deposits. The persistence of strombolian volcanic eruptions on Mount Cameroon and the particularly rainy context predispose it to other future episodes of lahar flow.

Crisis hazard assessment for snow-related lahars from an unforeseen new vent eruption: the 2018 eruption of Kusatsu-Shirane volcano, Japan

Two-thirds of the 111 active volcanoes in Japan are covered with snow for several months during winter and demonstrate high hazard and risk potentials associated with snow-related lahars during and after eruptions. On 23 January 2018, a sudden phreatic eruption occurred at the ski field on Kusatsu-Shirane (Mt. Motoshirane) volcano, Japan. This new vent eruption from the snow-clad pyroclastic cone required forecasting of future snow-related lahars and crisis hazards zonation of downslope areas including Kusatsu town, a popular tourist site for skiing and hot springs. In order to achieve a prompt hazard assessment for snow-related lahars, a multidisciplinary approach was carried out involving characterization of proximal tephra deposits, snow surveys, and numerical lahar flow simulations using the Titan2D model. To determine the input parameters for the flow model, the consideration of snow water equivalent (SWE) immediately after the eruption (on 29 January) and in the post-eruptive period (on 12 March), was significant. In the case of Kusatsu-Shirane volcano during the winter of 2018, linear relationships between altitude and SWE, obtained at different elevations, were used to estimate the snow volume around the new vents. Several scenarios incorporating snow and snowmelt (water), with or without the occurrence of a new eruption, were simulated for the prediction of future lahars. Three lahar scenarios were simulated, including A) rain-on-snow triggered, B) ice/snow slurry, and C) full snowmelt triggered by a new eruption, and indicated the flow paths (inundation areas) and travel distances. These were useful for lahar hazard zonation and identification of potential high-risk areas. Since the input parameters required for the Titan2D flow model can be relatively easily determined, the model was suitable for the 2018 eruption at Motoshirane where historical and geological lahar records are not available for calibration. The procedure used in the study will enable rapid lahar prediction and hazard zonation at snow-clad volcanoes. Further consideration for simulating a cohesive-type flow, which was predicted by the primary deposits containing large amounts of clay minerals and could not be expressed in the Titan2D flow model, is necessary.

Physical vulnerability assessment of settlements in lahar hazard prone areas along the river originated from Merapi Volcano

Merapi Vulcano is one of the most active volcanoes in the world. This volcano has a secondary hazard that is lahar flow. This research refers to the 2010 eruption of Merapi Vulcano in Indonesia. Eventhough there was a phreatic eruption in 2018, it did not increase the deposition of lahar material on its slopes. The communities living along the lahar prone rivers have various vulnerabilities including physical, social, economic and environmental vulnerability. This research aims to determine the physical vulnerability distribution of settlement in lahar hazard prone areas alongside Pabelan River. This study is a descriptive quantitative research using secondary data and spatial analysis. The results of this research show that the high vulnerability distribution covers the area of Mungkid Sub-district and Sawangan Sub-district as many as 5 clusters or equal to 7.49% of the research area. The medium level of physical vulnerability is Dukun Sub-district, Mungkid Sub-district and Muntilan Sub-district as many as 26 clusters or equal to 41.27% of the research area. The low physical vulnerability of settlements is scattered in Dukun Sub-district, Mungkid Sub-district, Muntilan Sub-district and Sawangan Sub-district as much as 32 clusters or equal to 50.79% of the research area. It can be concluded that the physical vulnerability of settlements in lahar hazar prone along the Pabelan river after the 2010 eruption of Merapi Vulcano is dominated by low vulnerability.

Tracking secondary lahar flow paths and characterizing pulses and surges using infrasound array networks at Volcán de Fuego, Guatemala

Lahars are one of the greatest hazards at many volcanoes, including Volcán de Fuego (Guatemala). On 1 December 2018 at 8:00pm local Guatemala time (2:00:00 UTC), an hour-long lahar event was detected at Volcán de Fuego by two permanent seismo-acoustic stations along the Las Lajas channel on the southeast side. To establish the timing, duration, and speed of the lahar, infrasound array records were examined to identify both the source direction(s) and the correlated energy fluctuations at the two stations. Co-located seismic and acoustic signals were also examined, which indicated at least 5 distinct energy pulses within the lahar record. We infer that varying sediment load and/or changes in flow velocity is shown by clear fluctuations in the acoustic and seismic power recorded at one of the stations. This particular event studied with infrasound provides insight into how lahars occur around Volcán de Fuego.

THE APPLICATION OF PYRAMID LUCAS-KANADE OPTICAL FLOW METHOD FOR TRACKING RAIN MOTION USING HIGH-RESOLUTION RADAR IMAGES

Short-duration rainfall characteristics in the form of certain intensity, time, and spatial distribution become valuable contribution for lahar flow disaster mitigation in a mountainous region. Due to mitigation purpose, such information can be provided through the rainfall nowcasting process. One of the promising rainfall nowcasting applications is the extrapolation-based method. Rain motion tracking is a crucial part of the rainfall nowcasting based on this method. This paper discusses the application of Pyramid Lucas-Kanade Optical Flow (PLKOF) method on the rain motion tracking analysis using 150x150m resolution radar image. The study of rain motion tracking is carried out using 112 successive rainfall images with 10-minutes time interval originating from Mt. Merapi X-band multiparameter radar. The rainfall movement patterns in short duration are presented in the displacement vector (u,v) images and scatter diagrams of rain motions at x- and y-directions. From the simulations, it was found that the average displacement of rain motions in the Mt. Merapi region is 9 pixels (8.3 km/h) with the dominant direction is northeast. The results show that PLKOF is relatively good at detecting small displacements, yet unable to identify the occurrence of rain growth and decay properly. The ability of PLKOF method in predicting the position of rain cell displacement is satisfied as indicated by the POD, CSI, and FAR indexes.

Sensitivity analysis of using unreliable rain gauge stations for evaluating the accuracy of radar rainfall estimates

Providing reliable rainfall information through the integration of all possible data sources such as rain gauge and radar can make a valuable contribution to the development of the lahar flow warning system. However, the reliability of radar rainfall (R) data still needs to be evaluated based on ground rainfall (G) given the estimated value of radar rainfall depth is not so precise compared to ground rainfall. The selection of which ground rainfall data can be used as an evaluation reference is based on the assessment of the variance analysis. Through the Scheffe test, the unreliable rain gauge stations can be known. The use of unreliable rain gauge stations for evaluating the accuracy of radar rainfall estimates affecting the parameter values of radar rainfall and ground rainfall conformity. This paper discusses sensitivity analysis of using unreliable rain gauge stations for evaluating the accuracy of radar rainfall estimates. Based on the Scheffe test, several scenarios are set to assess the change of conformity parameter values. The conformity between radar rainfall and ground rainfall are evaluated by using Log (G/R), FSE, and RMSE index. A number of 10-minute rainfall intensity data during 2016-2018 from 21 automatic rain gauge and X-band MP radar stations in the Merapi volcano region are used in the analysis. The result show that the less unreliable rain gauge stations used to assess the radar rainfall accuracy, the better the conformity parameter values.