Estimating Live Fuel Moisture Using SMAP L-Band Radiometer Soil Moisture for Southern California, USA

Shenyue Jia,Son V Nghiem,Menas Kafatos,Seung Hee Kim

doi:10.3390/rs11131575

Abstract

Live fuel moisture (LFM) is a field-measured indicator of vegetation water content and a crucial observation of vegetation flammability. This study presents a new multi-variant regression model to estimate LFM in the Mediterranean ecosystem of Southern California, USA, using the Soil Moisture Active Passive (SMAP) L-band radiometer soil moisture (SMAP SM) from April 2015 to December 2018 over 12 chamise (Adenostoma fasciculatum) LFM sites. The two-month lag between SMAP SM and LFM was utilized either as steps to synchronize the SMAP SM to the LFM series or as the leading time window to calculate the accumulative SMAP SM. Cumulative growing degree days (CGDDs) were also employed to address the impact from heat. Models were constructed separately for the green-up and brown-down periods. An inverse exponential weight function was applied in the calculation of accumulative SMAP SM to address the different contribution to the LFM between the earlier and present SMAP SM. The model using the weighted accumulative SMAP SM and CGDDs yielded the best results and outperformed the reference model using the Moderate Resolution Imaging Spectroradiometer (MODIS) Visible Atmospherically Resistance Index. Our study provides a new way to empirically estimate the LFM in chaparral areas and extends the application of SMAP SM in the study of wildfire risk.

Highlights

During the past decade, the increase of human activities in the wildland–urban interface (WUI) has raised the chance of wildfire in Southern California, USA, and elsewhere due to accelerated urbanization [1]
Soil Moisture Active Passive (SMAP) L-band SM products measure soil moisture residing in the top soil, which serves as a resSeMrvAoiPr fLo-rbansderiSeMs opf rpohdyusciotslomgiceaalsuproecseossilesmionisthtuergerroewsidngincgycinle tohfeptloapnts.oiSlM, wAhPicLh-bsaenrdveSsMas a respervovoiidrefdoraa nsewriespoosfspibhilyitsyiotloogciocanlstpruroctceesmsepsiriincatlhereggroeswsiionng mcyocdleelosf tpolaenstism. aStMe ALFPML,baankdeySM
Cumulative growing degree days (GDDs) (CGDD) as the second variable in the model addressed the heat needed during the growing cycle and the loss of topsoil moisture that influenced the change of Live fuel moisture (LFM)

Summary

Introduction

The increase of human activities in the wildland–urban interface (WUI) has raised the chance of wildfire in Southern California, USA, and elsewhere due to accelerated urbanization [1]. Combined with a recent extreme precipitation pattern under warmer climates, mega-fires have become more frequent [2]. Live fuel moisture (LFM) is a ratio of the amount of water contained in the fresh biomass to the weight of dry biomass [3]. The regular field observation of LFM in the U.S started in 1981. Local fire departments collect plant samples and input the measurements of LFM into a national system maintained by the United States Forest Service (USFS) [4]. LFM is used as a key input to the USFS National Fire Danger Rating System (NFDRS) [5]

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Conclusion