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For a connected reductive group G over a nonarchimedean local field F of positive characteristic, Genestier-Lafforgue and Fargues-Scholze have attached a semisimple parameter 
${\mathcal {L}}^{ss}(\pi )$ to each irreducible representation 
$\pi $. Our first result shows that the Genestier-Lafforgue parameter of a tempered 
$\pi $ can be uniquely refined to a tempered L-parameter 
${\mathcal {L}}(\pi )$, thus giving the unique local Langlands correspondence which is compatible with the Genestier-Lafforgue construction. Our second result establishes ramification properties of 
${\mathcal {L}}^{ss}(\pi )$ for unramified G and supercuspidal 
$\pi $ constructed by induction from an open compact (modulo center) subgroup. If 
${\mathcal {L}}^{ss}(\pi )$ is pure in an appropriate sense, we show that 
${\mathcal {L}}^{ss}(\pi )$ is ramified (unless G is a torus). If the inducing subgroup is sufficiently small in a precise sense, we show 
$\mathcal {L}^{ss}(\pi )$ is wildly ramified. The proofs are via global arguments, involving the construction of Poincaré series with strict control on ramification when the base curve is 
${\mathbb {P}}^1$ and a simple application of Deligne’s Weil II.
Let 
$G$ be a split semisimple group over a global function field 
$K$. Given a cuspidal automorphic representation 
$\Pi$ of 
$G$ satisfying a technical hypothesis, we prove that for almost all primes 
$\ell$, there is a cyclic base change lifting of 
$\Pi$ along any 
$\mathbb {Z}/\ell \mathbb {Z}$-extension of 
$K$. Our proof does not rely on any trace formulas; instead it is based on using modularity lifting theorems, together with a Smith theory argument, to obtain base change for residual representations. As an application, we also prove that for any split semisimple group 
$G$ over a local function field 
$F$, and almost all primes 
$\ell$, any irreducible admissible representation of 
$G(F)$ admits a base change along any 
$\mathbb {Z}/\ell \mathbb {Z}$-extension of 
$F$. Finally, we characterize local base change more explicitly for a class of toral representations considered in work of Chan and Oi.
