---
license: mit
base_model: Qwen/Qwen3-4B-Instruct-2507
language:
- en
library_name: transformers
pipeline_tag: text-generation
tags:
- hydrology
- agent
- tool-use
- grpo
- reinforcement-learning
- qwen3
- ef5
- crest
- function-calling
datasets:
- anonymousOwl/HydroAgent-dataset
---

# HydroAgent — Qwen3-4B-Instruct fine-tuned for hydrologic model calibration

**HydroAgent** is a tool-using language model that calibrates the
[EF5/CREST](https://github.com/HyDROSLab/EF5) distributed hydrologic model.
Given a USGS streamflow gage and a precipitation-driven simulation, the agent
iteratively proposes physically plausible parameter sets, runs the simulator,
inspects the resulting NSE / peak / volume metrics, and revises until the
model fits the observations.

This release is the **GRPO step-100 checkpoint** of the SFT + RL pipeline
described in [chrimerss/HydroLLM](https://github.com/chrimerss/HydroLLM).

- **Base model:** [`Qwen/Qwen3-4B-Instruct-2507`](https://huggingface.co/Qwen/Qwen3-4B-Instruct-2507)
- **Training:** full fine-tuning, BF16, FSDP, no LoRA
- **RL framework:** [verl 0.5](https://github.com/volcengine/verl) GRPO with [SGLang](https://github.com/sgl-project/sglang) rollouts
- **Tool format:** Hermes-style `<tool_call>` JSON (Qwen3-Instruct native)
- **Hardware:** 4× H100, ~30 min/step, K=6 rollouts × max 50 multi-turn calls

## How the agent works

The model has access to three tools and runs a multi-turn calibration loop:

| Tool | Purpose |
|---|---|
| `set_parameters` | Set 11 tunable CREST multipliers: `wm`, `b`, `im`, `ke`, `fc`, `under`, `leaki`, `alpha`, `beta`, `alpha0`, `iwu` |
| `run_simulation` | Execute EF5 with the current parameters and produce a hydrograph |
| `evaluate` | Score the latest run vs. observations: NSE, CC, KGE, peak ratio, lag |

Each rollout typically follows: `set_parameters → run_simulation → evaluate → set_parameters → …`
until NSE plateaus or the agent runs out of turns. Inputs to the agent are a
short system prompt describing the calibration task and a per-gage user
message with watershed metadata (basin area, lat/lon, time window).

## Training data

Training calibrates the agent on **10 CONUS USGS gages** (basin areas
539 – 2401 km²), each driven by **MRMS 1 km hourly precipitation** and
**hourly USGS streamflow observations** from 60-day windows selected to
contain a clear flood event (rising + receding limbs, edge-buffered).

| Gage ID | Basin (km²) | Lat | Lon | Window (UTC) |
|---|---:|---:|---:|---|
| 11383500 |  539 | 40.0140 | -121.9483 | 2018-05-19 → 2018-07-17 |
| 11043000 |  575 | 33.4798 | -117.1439 | 2019-03-15 → 2019-05-13 |
| 11152000 |  632 | 36.2805 | -121.3227 | 2018-05-29 → 2018-07-27 |
| 02294781 | 1064 | 27.8245 |  -81.8017 | 2018-04-29 → 2018-06-27 |
| 02312000 | 1476 | 28.4800 |  -82.1776 | 2018-11-15 → 2019-01-13 |
| 07195430 | 1489 | 36.1086 |  -94.5333 | 2018-01-04 → 2018-03-04 |
| 11179000 | 1639 | 37.5871 | -121.9608 | 2018-06-03 → 2018-08-01 |
| 14301000 | 1727 | 45.7040 | -123.7554 | 2018-09-11 → 2018-11-09 |
| 14207500 | 1828 | 45.3507 | -122.6762 | 2018-04-09 → 2018-06-07 |
| 11376000 | 2401 | 40.3871 | -122.2386 | 2018-09-21 → 2018-11-19 |

**Held-out evaluation gages** (never seen during training):

| Gage ID | Basin (km²) | Lat | Lon | Window (UTC) |
|---|---:|---:|---:|---|
| 02338660 |   329 | 33.2357 |  -84.9876 | 2018-07-01 → 2018-08-31 |
| 01403060 |  2033 | 40.5511 |  -74.5483 | 2018-11-11 → 2019-01-09 |
| 06279500 | 40792 | 44.7585 | -108.1816 | 2018-06-13 → 2018-08-11 |
| 07144100 |  3209 | 37.8831 |  -97.4245 | 2019-03-30 → 2019-05-28 |

The full training dataset — CONUS terrain rasters, per-gage MRMS hourly
precipitation clips, USGS hourly streamflow observations, daily PET, the
EF5 control template, and the 73 GPT-4o calibration trajectories that seed
the SFT phase — is published as
[**anonymousOwl/HydroAgent-dataset**](https://huggingface.co/datasets/anonymousOwl/HydroAgent-dataset).
See that repo's README for the per-folder layout and provenance.

## Reward

Two reward layers shape the policy:

**Per-turn (returned by tools):**

| Tool call | Reward |
|---|---|
| `set_parameters` (valid) | `+0.02` |
| `run_simulation` (valid) | `+0.05` |
| `evaluate` (valid) | `ΔNSE` (this turn − previous best) |
| Any tool (invalid) | `−0.5` |

**Terminal (returned at end of trajectory):**

| Component | Value |
|---|---|
| Best NSE (clipped) | `[−1, 1]` |
| Target-met bonus | `+0.5` if best NSE > gage target |
| Iteration bonus | `+0.02 × n_evaluates` |
| Improvement bonus | `+0.10 × max(0, n_improvements − 1)` |
| Empty-trajectory penalty | `−1.0` |

## GRPO settings

| Setting | Value |
|---|---|
| Algorithm | GRPO (group-relative advantages) |
| K (rollouts per prompt) | 6 |
| Train batch size | 4 prompts (24 trajectories per step) |
| Max assistant turns | 50 |
| Learning rate | 1e-6 with 5% warmup |
| Entropy coefficient | 0.01 |
| KL loss coefficient | 0.05 (anchored to base policy) |
| Sampling | `temperature=1.0`, `top_p=0.95` |
| Steps in this checkpoint | **100** |

## Quick start

```python
from transformers import AutoModelForCausalLM, AutoTokenizer

repo = "anonymousOwl/HydroAgent"
tokenizer = AutoTokenizer.from_pretrained(repo, trust_remote_code=True)
model = AutoModelForCausalLM.from_pretrained(repo, torch_dtype="bfloat16", device_map="auto")
```

The model emits Hermes-style tool calls, e.g.:

```
<tool_call>
{"name": "set_parameters", "arguments": {"wm": 1.0, "b": 1.0, "im": 0.5, ...}}
</tool_call>
```

Parse with `tokenizer.apply_chat_template(..., tools=HYDRO_TOOLS)` and
dispatch each call to your EF5 sandbox. See
[`modal_app/eval.py`](https://github.com/chrimerss/HydroLLM/blob/main/modal_app/eval.py)
for a reference SGLang loop with retry-on-parse-failure logic.

For full reproduction (image, EF5 binary, multi-turn rollout, reward
computation), use the
[HydroLLM repository](https://github.com/chrimerss/HydroLLM).

## Limitations

- Trained on **10 small/medium CONUS basins** (≤ 2401 km²) over short flood
  windows. Generalization to large basins (> 3000 km²), arid catchments, or
  out-of-CONUS regions is unverified.
- Calibrates **CREST parameter multipliers only** — does not modify routing,
  initial conditions, or sub-basin structure.
- The agent depends on a working EF5 toolchain; the weights alone do not
  perform calibration without the simulation environment in the loop.
- This is a research checkpoint, not a production tool. NSE on held-out
  gages varies substantially with basin and event.

## License

MIT — same as the upstream [HydroLLM repository](https://github.com/chrimerss/HydroLLM)
and the base [Qwen3-4B-Instruct-2507](https://huggingface.co/Qwen/Qwen3-4B-Instruct-2507).

## Citation

```bibtex
@software{hydrollm2026,
  title  = {HydroLLM: Reinforcement Learning Fine-Tuning of LLMs with Hydrologic Simulation Feedback},
  year   = {2026},
  url    = {https://github.com/chrimerss/HydroLLM}
}
```

## Acknowledgement

Compute for this research was sponsored by [Modal](https://modal.com).