<p><strong>Abstract.</strong> Erhai Lake is a subtropical highland shallow lake on the southeast margin of the Tibetan Plateau, which is influenced by both South Asian and East Asian summer monsoons. Based on 4 years of continuous eddy covariance (EC) data over Erhai Lake, the monsoon effect on water–atmosphere exchange processes is investigated by comparing the energy and <span class="inline-formula">CO₂</span> flux patterns and their main drivers during pre-monsoon (March–April),

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... nsoon (May–October) and post-monsoon (November–December) periods. The results show that the atmospheric properties display a large difference during the three different periods. There is a negative difference between water surface and air temperature (<span class="inline-formula"><i>T</i></span>) during the pre-monsoon period, while a positive <span class="inline-formula"><i>T</i></span> during the post-monsoon period. The diurnal sensible heat flux (<span class="inline-formula"><i>H</i>_s</span>) is larger during the post-monsoon period, while the latent heat flux (LE) is larger during the monsoon period. The monthly average <span class="inline-formula"><i>H</i>_s</span> and heat storage (<span class="inline-formula"><i>Q</i></span>) in the lake remain negative during the pre-monsoon period and the early monsoon period, and they become positive in the middle monsoon period, which indicates that the lake absorbs heat at first and releases it subsequently. LE plays a dominating role in the energy partitioning of the lake. The Bowen ratio is higher during the post-monsoon period. The uptake of <span class="inline-formula">CO₂</span> flux is observed in the middle of the day during monsoon and post-monsoon periods. The <span class="inline-formula">Δ<i>T</i></span> is the main driver for <span class="inline-formula"><i>H</i>_s</span> and the effect of <span class="inline-formula">Δ<i>T</i></span> is increased as timescales are extended from half-hourly to monthly. The wind speed has a weak effect on <span class="inline-formula"><i>H</i>_s</span> but a strong effect on LE and <span class="inline-formula">CO₂</span> fluxes. Similar main drivers for <span class="inline-formula"><i>H</i>_s</span> are found during the pre-monsoon and post-monsoon periods, which is also found for <span class="inline-formula">CO₂</span> flux, indicating a large impact of the monsoon on the heat and carbon exchange processes over Erhai Lake.</p>