Simulasi fluks karbon dan air dengan Biome-BGC MuSo

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 Referensi : 

Min Y, Li ZY, Tian X, Zhang L, Zhou Y. 2019. Improved simulation of carbon and water fluxes by assimilating multi-layer soil temperature and moisture into process-based biogeochemical model. Forest Ecosystems, 6:12. DOI : https://doi.org/10.1186/s40664-019-0171-5.


Latar belakang : Suhu dan kelembaban tanah merupakan indikator yang sensitif di dalam dekomposisi materi organik tanah karena keduanya mengendalkan siklus karbon dan air global dan memberikan umpan balik yang potensial bagi variasi iklim. Meskipun model Biome-Biogeochemical Cycles (Biome-BGC) telah secara luas diterapkan di dalam simulasi fluks karbon dan air hutan, modul tanah satu lapisnya tidak mampu menjelaskan variasi vertikal di dalam kelembaban tanah. Penelitian ini memperkenalkan model Biome-BGC MuSo yang terdiri atas modul tanah multi-layer dan modul-modul baru yang dapat menjelaskan fenologi dan pengelolaan untuk simulasi fluks karbon dan air. Meskipun model ini menitikberatkan pada proses-proses tanah pada lapisan-lapisan yang aktif, estimasi variabel-variabel yang berhubungan dengan tanah dapat mengalami bias sehingga menghasilkan estimasi yang tidak akurat tentang fluks karbon dan air. 

Metode : Guna memperbaiki estimasi proses-proses yang berkenaan dengan tanah di dalam Biome-BGC MuSo, penelitian ini menghasimilasikan suhu dan kelembaban tanah harian ground-measure multi-layer pada lokasi fluks Pegunungan Changbai dengan menggunakan algoritma Ensemble Kalman Filter. Estimasi fluks tanah dan karbon pada model dievaluasi dengan ukuran koefisien determinasi (R²) dan root mean square error (RMSE). Penelitian kemudian berlanjut dengan menghitung RMSE dari Biome-BGC MuSo dan Biome-BGC MuSo terasimilasi dihitung (DeltaRMSE), dan analisis terhadap hubungan antara DeltaRMSE dan faktor-faktor iklim dan biofisika.

Hasil : Dibandingkan model Biome-BGC yang sebelu⁻¹mnya, Biome-BGC MuSo memperbaiki simulasi respirasi ekosistem (ER), net ecosystem exchange (NEE) dan evapotranspirasi (ET). Asimilasi data dari variabel-variabel terkait tanah ke dalam Biome-BGC MuSo di dalam real time meningkatkan akurasi fluks karbon dan air yang disimulasi (ET: R² = 0,81, RMSE = 0,70 mmd⦁d⁻² ; ER: R⁻² = 0,85, RMSE = 1,97 gC⦁m⁻²⦁d ; NEE: R² = 0,70, RMSE = 1,16 gC.m⁻²⦁d⁻¹).

Simpulan : Penelitian ini membuktikan bahwa simulasi musiman fluks karbon dan tanah lebih akurat pada saat menggunakan Biome-BGC MuSo dengan modul tanah multi-layer daripada menggunakan Biome-BGC dengan modul single-layer. Lebih lanjut, dengan mengasimilasikan data suhu dan kelembaban tanah ke dalam Biome-BGC MuSo, penelitian ini berhasil memperbaiki estimasi fluks air dan karbon pada modul melalui simulasi-simulasi terkait dengan tanah yang dikalibrasi. Strategi asimilasi berlaku untuk berbagai kondisi iklim dan biofisika, khususnya pada daerah hutan lebat, dan untuk simulasi lokal atau regional.

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