Modification of a fire drought index for tropical wetland ecosystems by including water table depth

Abstract

a b s t r a c tIn this paper, we discuss how an existing empirical drought index, i.e. the Keetch-Byram Drought Index (KBDI) that is commonly used for assessing forest fire danger, has been adjusted and modified for improved use in tropical wetland ecosystems. The improvement included: (i) adjustment of the drought factor to the local climate, and (ii) addition of the water table depth as a dynamic factor to control the drought index. We distinguished three different indices, the original Keetch-Byram Drought Index, the adjusted KBDI (KBDI adj ) that represents the original drought index, but including local climate information, and the modified KBDI (mKBDI) that considers both local climate information, and soil and hydrological characteristics. The mKBDI was developed and tested in a wetland forest of South Sumatra (Indonesia) from April 2009 to March 2011. During this period, hydrometeorological data were monitored and used to calculate the KBDI, KBDI adj , and mKBDI. First, mKBDI was calibrated using observed soil moisture that was converted to an observed drought index (DI obs ). The results indicate that performance of the mKBDI is encouraging based on the following: (i) its pattern followed the dynamics of DI obs , (ii) prediction of frequency of fire danger classes, and (iii) statistically criteria. The mKBDI clearly outperformed KBDI and KBDI adj . Furthermore, we found a critical water table depth when it reaches maximum fire danger (0.85 m for the wetland forest of South Sumatra) below which danger does not increase anymore. The mKBDI could be more widely applied, if pedotransfer functions are developed that link easily obtainable soil properties to the parameters of the water table factor. Our findings encourage land use planners, water managers and stakeholders (e.g. forest estate owners) to integrate local climate information, and soil and hydrological characteristics into the Keetch-Byram Drought Index to better predict fire danger, particularly in tropical wetland ecosystems.

Hydrological drought explained

“…Examples of affected sectors are drinking water supply, crop production (irrigation), waterborne transportation, electricity production (hydropower or cooling water), and recreation (water quality) e.g., Refs . The ecosystem impacts of drought differ between terrestrial ecosystems, in which droughts influence tree mortality due to wild fires, and aquatic ecosystems, where they affect e.g., species composition, population density, and food web structure . Examples of drought events in the recent and distant past and their impacts are provided in Box .…”

Tingkat Kerawanan Kebakaran Gambut Di Kabupaten Musi Banyuasin, Sumatera Selatan

“…Pada kondisi alami, gambut jenuh akan air. Tetapi pada kondisi gambut terdegradasi akibat pembukaan hutan, pembuatan drainase, air gambut akan dengan mudah mengalir keluar, sehingga gambut menjadi kering (Turetsky et al, 2015;Taufik, Setiawan, & Lanen, 2015). Bahan organik pada kondisi ke-ring dan saat kemarau panjang akan sangat mudah terbakar.…”

“…Gambut dapat menyerap air 1 hingga 13 kali bobotnya (Dariah, Maftuah, & Maswar, 2011). Akan tetapi, gambut yang telah ditebang vegetasinya dan dibangun drainase atau kanal sehingga air gambut terkuras, menyebabkan kondisi gambut berubah menjadi kering dan lapisan permukaan gambut menjadi lebih padat (subsiden) (Dariah et al, 2011), (Taufik et al, 2015). Hal ini menyebabkan gambut terdrainase menjadi rawan kebakaran (Syaufina, 2008), (Taufik et al, 2015), (Turetsky et al, 2015), (S. Page, 2016) (S. Page, 2016).…”

“…Gambut merupakan bahan organik yang pada musim kemarau dan kondisi kering merupakan bahan bakar yang mudah terbakar ( (Syaufina, 2008), (Heriyanto et al, 2014), (Taufik et al, 2015)). Kondisi ini diperparah oleh kebiasaan masyarakat membuka kebun dan ladang dengan cara membakar vegetasi rumput, semak dan/atau belukar (Elysa, 2014 Dalam kaitan dengan pengelolaan ekosistem gambut, menurut PP.57 tahun 2016 tentang Perlindungan dan Pengelolaan Ekosistem Gambut, masih mengatur tinggi muka air (TMA) tanah tidak lebih dari 40 cm pada fungsi budidaya.…”

“…Berbagai laporan menunjukkan bahwa penyekatan kanal dan rewetting dapat meningkatkan tinggi muka air tanah, sehingga dapat menurunkan emisi gas CO2, memperlambat subsidensi (Wösten, Clymans, Page, Rieley, & Limin, 2008;Ritzema, Limin, Kusin, Jauhiainen, & Wösten, 2014;Jauhiainen, Page, & Vasander, 2016); dan dapat mengurangi kejadian kebakaran (Evers, Yule, Padfield, O'Reilly, & Varkkey, 2016;Taufik et al, 2015).…”