In just four lines, the speaker looks back on a choice, or perhaps a discovery, made young. "Early on" suggests a turning point in childhood or youth, when they found something unexpected in melancholy. Instead of treating sadness as something to escape, they describe it as water: smooth, soft, almost luxurious. The word "velvet" is surprising, since we usually think of sadness as heavy or rough, not pleasant to touch.
The final phrase, "the best cold life," holds a tension. Cold usually suggests distance or loneliness, yet "best" signals real satisfaction. The speaker seems to say that a quiet, reflective, somewhat solitary way of living suited them better than warmth or cheer would have.
The title, "Hydrologic," plays on the study of water and on the word "logic," as if this attraction to sorrow follows its own natural reasoning. The mood is calm, cool, and contemplative, with no self-pity, only a quiet acceptance.