Subseasonal-to-Seasonal Monsoon Forecasting
IRI for Climate and Society, Columbia
with Prof. Andrew Robertson
Collaborators · Andrew Robertson · Muhammad Azhar Ehsan · Mohammad Erfani · Emile Dara Esmaili · Haoxi
11+
Model variants
~47%
Leak share of skill
0.039 vs 0.012
Best RPSS vs. ELR baseline
- 01
Built FiLM-conditioned U-Net models for Week 3–4 Indian monsoon rainfall forecasting, ablating conditioning across MJO, SST/Niño3.4 and IOD with FiLM vs. broadcast conditioning. The best model (IOD+SST+MJO, FiLM) reached RPSS 0.039 — roughly 3× the extended-logistic-regression baseline (0.012).
- 02
Discovered a data-alignment leak — conditioning indices matched to the target window instead of the issue date — and built a per-sample diagnostic exposing it (~47% of apparent skill; RPSS 0.047 → 0.025). Proposed an operationally valid fix: conditioning on issue-time predicted indices (e.g., IITM's predicted MISO).
- 03
Replaced bootstrapping with deterministic leave-3-years-out cross-validation and evaluated skill per grid cell with spatial skill maps, documenting negative results without overclaiming.
Fig. 1 — Where the skill went
Conditioning indices were aligned to the target window, not the forecast issue date.
A per-sample diagnostic showed roughly 47% of apparent RPSS came from information a forecaster wouldn't have on issue day. The fix: issue-time predicted indices — operationally valid, honestly lower.





